feat(account): danger zone, restore import, larger API key field on phones

- Danger zone in settings: delete all own data or the account, both with
  password confirmation; the last server admin cannot delete the account
- DELETE /user/data and /user/account; PurgeUserData removes everything a
  user owns in one transaction (others' tasks in shared lists stay theirs),
  also used by admin user deletion
- MindSift import: 'Hinzufügen' or 'Wiederherstellen' (mode=restore, wipes
  own data only after the file is fully validated, confirm checkbox)
- API key name field and button 44 px on phones (flex-1 collapsed them)

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

frontend/src/features/settings/ImportCard.tsx

@@ -30,11 +30,16 @@ export const ImportCard: React.FC<ImportCardProps> = ({ source, title, descripti
   const [busy, setBusy] = useState(false);
   const [error, setError] = useState<string | null>(null);
   const [dragOver, setDragOver] = useState(false);
+  // MindSift data can replace the current state instead of being added next to it
+  const [mode, setMode] = useState<'merge' | 'restore'>('merge');
+  const [confirmRestore, setConfirmRestore] = useState(false);
+  const restoring = source === 'mindsift' && mode === 'restore';
 
   const reset = () => {
     setFile(null);
     setPreview(null);
     setError(null);
+    setConfirmRestore(false);
   };
 
   const pick = async (f?: File) => {
@@ -57,9 +62,10 @@ export const ImportCard: React.FC<ImportCardProps> = ({ source, title, descripti
     setBusy(true);
     setError(null);
     try {
-      setResult(await api.importData(source, file, false));
+      setResult(await api.importData(source, file, false, restoring ? 'restore' : 'merge'));
       setFile(null);
       setPreview(null);
+      setConfirmRestore(false);
     } catch (err: any) {
       setError(err.message || 'Import fehlgeschlagen');
     } finally {
@@ -76,6 +82,38 @@ export const ImportCard: React.FC<ImportCardProps> = ({ source, title, descripti
         <p className="text-muted text-[11px] mt-0.5">{description}</p>
       </div>
 
+      {source === 'mindsift' && (
+        <div className="grid grid-cols-1 sm:grid-cols-2 gap-2" role="radiogroup" aria-label="Import-Modus">
+          {(
+            [
+              ['merge', 'Hinzufügen', 'Bestehende Daten behalten, Backup daneben anlegen.'],
+              ['restore', 'Wiederherstellen', 'Eigene Notizen, Aufgaben und Listen vorher löschen.'],
+            ] as const
+          ).map(([value, label, text]) => (
+            <button
+              key={value}
+              type="button"
+              role="radio"
+              aria-checked={mode === value}
+              onClick={() => {
+                setMode(value);
+                setConfirmRestore(false);
+              }}
+              className={`p-2.5 min-h-[44px] text-left border rounded-card transition-colors ${
+                mode === value
+                  ? value === 'restore'
+                    ? 'border-status-err bg-status-err/10'
+                    : 'border-accent bg-accent/10'
+                  : 'border-border hover:border-strong'
+              }`}
+            >
+              <span className={`block text-xs font-semibold ${value === 'restore' && mode === value ? 'text-status-err' : 'text-main'}`}>{label}</span>
+              <span className="block text-[11px] text-muted">{text}</span>
+            </button>
+          ))}
+        </div>
+      )}
+
       <div
         onDragOver={(e) => {
           e.preventDefault();
@@ -147,10 +185,30 @@ export const ImportCard: React.FC<ImportCardProps> = ({ source, title, descripti
               </ul>
             </details>
           )}
+          {!result && restoring && (
+            <label className="flex items-start gap-2 p-2.5 rounded-card border border-status-err/40 bg-status-err/10 text-[11px] text-main cursor-pointer">
+              <input
+                type="checkbox"
+                checked={confirmRestore}
+                onChange={(e) => setConfirmRestore(e.target.checked)}
+                className="mt-0.5 w-4 h-4 shrink-0"
+              />
+              <span>
+                <strong className="text-status-err">Achtung:</strong> Alle deine bisherigen Notizen, Ordner, Aufgaben, Gedanken und
+                Listen werden vor dem Import unwiderruflich gelöscht und durch das Backup ersetzt. Mit dir geteilte Inhalte anderer
+                bleiben erhalten.
+              </span>
+            </label>
+          )}
           {!result && (
             <div className="flex flex-col sm:flex-row gap-2 pt-1">
-              <button type="button" onClick={runImport} className="btn-primary h-11 sm:h-8 px-4 text-xs font-semibold">
-                Jetzt importieren
+              <button
+                type="button"
+                onClick={runImport}
+                disabled={restoring && !confirmRestore}
+                className={`h-11 sm:h-8 px-4 text-xs font-semibold disabled:opacity-50 ${restoring ? 'btn-action border-status-err text-status-err' : 'btn-primary'}`}
+              >
+                {restoring ? 'Löschen und wiederherstellen' : 'Jetzt importieren'}
               </button>
               <button type="button" onClick={reset} className="btn-action h-11 sm:h-8 px-3 text-xs">
                 Abbrechen