feat(themes): custom CSS themes per user (upload, paste, live)

- Theme manager in settings: upload a .css file or paste CSS, template
  download/copy/insert, edit and delete; custom themes show up in the
  gallery and the quick switchers
- Themes are injected live as <style id="mindsift-custom-theme">; the
  active one is cached so it applies on boot without flashing
- Backend: user_themes table and GET/POST /themes, DELETE /themes/{id}
  (per user, max 200 KB)
- Docs: theming, REST, database

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

frontend/src/features/settings/UserSettingsView.tsx

@@ -17,16 +17,22 @@ import {
   Palette,
   Upload,
   Camera,
+  Pencil,
+  Copy,
 } from 'lucide-react';
-import { APIKey, User } from '../../lib/types';
+import { APIKey, User, UserTheme } from '../../lib/types';
 import { api, triggerHaptic } from '../../lib/api';
-import { AVAILABLE_THEMES, ThemeId } from '../../lib/theme';
+import { customThemeId, ThemeId, ThemeOption } from '../../lib/theme';
+import themeTemplateCss from '../../themes/theme-template.css?raw';
 import { UserAvatar, resizeImageToDataUrl } from '../../components/UserAvatar';
 
 interface UserSettingsViewProps {
   currentUser: User;
   activeTheme: ThemeId;
+  themes: ThemeOption[]; // built-in + custom
+  customThemes: UserTheme[];
   onThemeChange: (themeId: ThemeId) => void;
+  onCustomThemesChange: (themes: UserTheme[], activate?: ThemeId) => void;
   onUserUpdated: (u: User) => void;
   onBack: () => void;
 }
@@ -36,12 +42,98 @@ type UserSettingsSection = 'profile' | 'appearance' | 'alarms' | 'webhooks';
 export const UserSettingsView: React.FC<UserSettingsViewProps> = ({
   currentUser,
   activeTheme,
+  themes,
+  customThemes,
   onThemeChange,
+  onCustomThemesChange,
   onUserUpdated,
   onBack,
 }) => {
   const [section, setSection] = useState<UserSettingsSection>('profile');
 
+  // --- Custom Theme Editor State ---
+  const [themeEditId, setThemeEditId] = useState<string | null>(null); // null = new theme
+  const [themeName, setThemeName] = useState('');
+  const [themeCss, setThemeCss] = useState('');
+  const [themeMsg, setThemeMsg] = useState<{ type: 'ok' | 'err'; text: string } | null>(null);
+  const [savingTheme, setSavingTheme] = useState(false);
+  const [deletingThemeId, setDeletingThemeId] = useState<string | null>(null);
+  const themeFileRef = useRef<HTMLInputElement>(null);
+
+  const resetThemeEditor = () => {
+    setThemeEditId(null);
+    setThemeName('');
+    setThemeCss('');
+  };
+
+  const handleThemeFile = async (file?: File) => {
+    if (!file) return;
+    const text = await file.text();
+    setThemeCss(text);
+    if (!themeName.trim()) setThemeName(file.name.replace(/\.css$/i, '').replace(/^theme-/, ''));
+    setThemeMsg(null);
+  };
+
+  const handleDownloadTemplate = () => {
+    const url = URL.createObjectURL(new Blob([themeTemplateCss], { type: 'text/css' }));
+    const a = document.createElement('a');
+    a.href = url;
+    a.download = 'theme-template.css';
+    a.click();
+    URL.revokeObjectURL(url);
+  };
+
+  const handleCopyTemplate = async () => {
+    try {
+      await navigator.clipboard.writeText(themeTemplateCss);
+      setThemeMsg({ type: 'ok', text: 'Vorlage in die Zwischenablage kopiert.' });
+    } catch {
+      setThemeMsg({ type: 'err', text: 'Kopieren nicht möglich – nutze „Vorlage einfügen“ oder den Download.' });
+    }
+  };
+
+  // Saving activates the theme right away (injected live, no reload)
+  const handleSaveTheme = async (e: React.FormEvent) => {
+    e.preventDefault();
+    setSavingTheme(true);
+    setThemeMsg(null);
+    try {
+      const saved = await api.saveTheme({ id: themeEditId || undefined, name: themeName.trim(), css: themeCss });
+      const next = themeEditId
+        ? customThemes.map((t) => (t.id === saved.id ? saved : t))
+        : [...customThemes, saved];
+      onCustomThemesChange(next, customThemeId(saved));
+      setThemeMsg({ type: 'ok', text: `Theme „${saved.name}“ gespeichert und aktiviert.` });
+      resetThemeEditor();
+    } catch (err: any) {
+      setThemeMsg({ type: 'err', text: err.message || 'Theme konnte nicht gespeichert werden' });
+    } finally {
+      setSavingTheme(false);
+    }
+  };
+
+  const handleEditTheme = (t: UserTheme) => {
+    setThemeEditId(t.id);
+    setThemeName(t.name);
+    setThemeCss(t.css);
+    setThemeMsg(null);
+  };
+
+  const handleDeleteTheme = async (t: UserTheme) => {
+    try {
+      await api.deleteTheme(t.id);
+      setDeletingThemeId(null);
+      if (themeEditId === t.id) resetThemeEditor();
+      // Deleting the active theme falls back to the default one
+      onCustomThemesChange(
+        customThemes.filter((x) => x.id !== t.id),
+        activeTheme === customThemeId(t) ? 'dark' : undefined
+      );
+    } catch (err: any) {
+      setThemeMsg({ type: 'err', text: err.message || 'Theme konnte nicht gelöscht werden' });
+    }
+  };
+
   // --- Profile State ---
   const [displayName, setDisplayName] = useState(currentUser.displayName || '');
   const [email, setEmail] = useState(currentUser.email || '');
@@ -591,14 +683,15 @@ export const UserSettingsView: React.FC<UserSettingsViewProps> = ({
               </div>
 
               <div className="grid grid-cols-1 sm:grid-cols-2 gap-3">
-                {AVAILABLE_THEMES.map((t) => {
+                {themes.map((t) => {
                   const isSelected = activeTheme === t.id;
+                  const custom = customThemes.find((c) => customThemeId(c) === t.id);
                   return (
+                    <div key={t.id} className="flex flex-col">
                     <button
-                      key={t.id}
                       type="button"
                       onClick={() => onThemeChange(t.id)}
-                      className={`p-4 text-left border transition-all flex flex-col justify-between gap-3 ${
+                      className={`flex-1 p-4 text-left border transition-all flex flex-col justify-between gap-3 ${
                         isSelected
                           ? 'bg-canvas border-accent shadow-sm'
                           : 'bg-canvas border-border hover:border-strong'
@@ -654,23 +747,130 @@ export const UserSettingsView: React.FC<UserSettingsViewProps> = ({
                         <code className="text-[10px] font-mono text-faint">{t.file}</code>
                       </div>
                     </button>
+                    {custom && (
+                      <div className="flex items-center justify-end gap-1.5 px-2 py-1.5 border border-t-0 border-border bg-canvas">
+                        {deletingThemeId === custom.id ? (
+                          <>
+                            <span className="flex-1 text-[11px] text-muted">Theme wirklich löschen?</span>
+                            <button onClick={() => handleDeleteTheme(custom)} className="btn-primary h-7 px-2.5 text-[11px]">
+                              Löschen
+                            </button>
+                            <button onClick={() => setDeletingThemeId(null)} className="btn-action h-7 px-2 text-[11px]">
+                              Abbrechen
+                            </button>
+                          </>
+                        ) : (
+                          <>
+                            <button onClick={() => handleEditTheme(custom)} className="btn-icon" title="Theme bearbeiten">
+                              <Pencil className="w-3.5 h-3.5" />
+                            </button>
+                            <button
+                              onClick={() => setDeletingThemeId(custom.id)}
+                              className="btn-icon btn-icon-danger"
+                              title="Theme löschen"
+                            >
+                              <Trash2 className="w-3.5 h-3.5" />
+                            </button>
+                          </>
+                        )}
+                      </div>
+                    )}
+                    </div>
                   );
                 })}
               </div>
 
-              <div className="p-3.5 bg-canvas border border-border space-y-1.5">
-                <p className="font-semibold text-main">Eigenes Theme anpassen oder hinzufügen:</p>
+              {/* Custom theme: upload or paste CSS, based on the template */}
+              <form onSubmit={handleSaveTheme} className="p-4 bg-canvas border border-border space-y-3">
+                <div className="flex flex-wrap items-center justify-between gap-2">
+                  <p className="font-semibold text-main">
+                    {themeEditId ? 'Eigenes Theme bearbeiten' : 'Eigenes Theme hinzufügen'}
+                  </p>
+                  <div className="flex flex-wrap gap-1.5">
+                    <button type="button" onClick={handleDownloadTemplate} className="btn-action h-7 px-2 text-[11px] flex items-center gap-1">
+                      <Download className="w-3 h-3" />
+                      <span>Vorlage herunterladen</span>
+                    </button>
+                    <button type="button" onClick={handleCopyTemplate} className="btn-action h-7 px-2 text-[11px] flex items-center gap-1">
+                      <Copy className="w-3 h-3" />
+                      <span>Vorlage kopieren</span>
+                    </button>
+                    <button
+                      type="button"
+                      onClick={() => setThemeCss(themeTemplateCss)}
+                      className="btn-action h-7 px-2 text-[11px]"
+                    >
+                      Vorlage einfügen
+                    </button>
+                  </div>
+                </div>
+
                 <p className="text-muted text-[11px] leading-relaxed">
-                  Alle Theme-Dateien liegen unter{' '}
-                  <code className="font-mono text-accent">frontend/src/themes/</code> (inklusive der
-                  Kopiervorlage{' '}
-                  <code className="font-mono text-accent">theme-template.css</code>). Dort sind alle
-                  Eigenschaften in 6 Blöcken gruppiert: <strong>1. Akzentfarbe</strong>,{' '}
-                  <strong>2. Oberflächen</strong>, <strong>3. Textfarben</strong>,{' '}
-                  <strong>4. Rahmen &amp; Schatten</strong>, <strong>5. Statusfarben</strong> und{' '}
-                  <strong>6. Rundungen</strong>.
+                  Ein Theme ist CSS mit 6 Blöcken: <strong>1. Akzentfarbe</strong>, <strong>2. Oberflächen</strong>,{' '}
+                  <strong>3. Textfarben</strong>, <strong>4. Rahmen &amp; Schatten</strong>, <strong>5. Statusfarben</strong> und{' '}
+                  <strong>6. Rundungen</strong>. Am einfachsten startest du mit der Vorlage und änderst die Werte. Gespeicherte
+                  Themes liegen auf dem Server und stehen dir auf allen Geräten zur Verfügung.
                 </p>
-              </div>
+
+                <div className="flex flex-col sm:flex-row gap-2">
+                  <input
+                    type="text"
+                    value={themeName}
+                    onChange={(e) => setThemeName(e.target.value)}
+                    placeholder="Name, z. B. Wald"
+                    maxLength={60}
+                    className="flex-1 min-w-0 h-8 px-2.5 input-field"
+                  />
+                  <button
+                    type="button"
+                    onClick={() => themeFileRef.current?.click()}
+                    className="btn-action h-8 px-3 text-xs flex items-center justify-center gap-1.5"
+                  >
+                    <Upload className="w-3.5 h-3.5" />
+                    <span>CSS-Datei hochladen</span>
+                  </button>
+                  <input
+                    ref={themeFileRef}
+                    type="file"
+                    accept=".css,text/css"
+                    className="hidden"
+                    onChange={(e) => {
+                      handleThemeFile(e.target.files?.[0]);
+                      e.target.value = '';
+                    }}
+                  />
+                </div>
+
+                <textarea
+                  value={themeCss}
+                  onChange={(e) => setThemeCss(e.target.value)}
+                  placeholder=":root[data-theme=&quot;mein-theme&quot;] { --accent-primary: #15803d; … }"
+                  rows={10}
+                  spellCheck={false}
+                  className="w-full px-2.5 py-2 input-field font-mono text-[11px] leading-relaxed resize-y"
+                />
+
+                {themeMsg && (
+                  <p className={`text-[11px] ${themeMsg.type === 'ok' ? 'text-status-ok' : 'text-status-err'}`}>
+                    {themeMsg.text}
+                  </p>
+                )}
+
+                <div className="flex justify-end gap-2">
+                  {themeEditId && (
+                    <button type="button" onClick={resetThemeEditor} className="btn-action h-8 px-3 text-xs">
+                      Abbrechen
+                    </button>
+                  )}
+                  <button
+                    type="submit"
+                    disabled={savingTheme || !themeName.trim() || !themeCss.trim()}
+                    className="btn-primary h-8 px-4 text-xs font-semibold disabled:opacity-50"
+                  >
+                    {savingTheme ? 'Speichere…' : 'Speichern & aktivieren'}
+                  </button>
+                </div>
+              </form>
             </div>
           )}