feat(workspace): journal with one note per day and a calendar

- journal_days (migration 8) maps a person's day to an ordinary note;
  GET /journal lists the days, POST /journal/{date} opens or creates one
- the journal sits on top of the notes sidebar: days below each other
  (today first, older ones load while scrolling), a calendar with month
  and year picker follows the day in view and jumps to any day
- the header shares the day in view; journal notes stay out of the folder
  tree; can be switched off per device under Darstellung

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

frontend/src/features/settings/UserSettingsView.tsx

@@ -32,6 +32,7 @@ import { ImportCard } from './ImportCard';
 import { SessionsPanel } from './SessionsPanel';
 import { ToggleSwitch } from '../../components/ToggleSwitch';
 import { setLinkPreviewsEnabled, useLinkPreviewsEnabled } from '../../lib/linkPreview';
+import { isJournalEnabled, setJournalEnabled } from '../../lib/journal';
 import { FormSheet } from '../../components/FormSheet';
 
 interface UserSettingsViewProps {
@@ -150,6 +151,7 @@ export const UserSettingsView: React.FC<UserSettingsViewProps> = ({
   // The public demo sends nothing and keeps the shared accounts intact (FLAW-33)
   const [demoMode, setDemoMode] = useState(false);
   const linkPreviewsOn = useLinkPreviewsEnabled();
+  const [journalOn, setJournalOn] = useState(isJournalEnabled);
   useEffect(() => {
     api
       .getAuthStatus()
@@ -854,6 +856,24 @@ export const UserSettingsView: React.FC<UserSettingsViewProps> = ({
                 <ToggleSwitch checked={linkPreviewsOn} onChange={setLinkPreviewsEnabled} title="Link-Vorschauen anzeigen" />
               </div>
 
+              <div className="p-3.5 rounded-card border border-border bg-canvas flex items-center justify-between gap-4">
+                <div className="text-xs">
+                  <p className="font-semibold text-main">Journal anzeigen</p>
+                  <p className="text-[11px] text-faint">
+                    Eine Notiz pro Tag, untereinander mit Kalender – ganz oben in der Notizen-Seitenleiste. Ausschalten
+                    blendet es nur aus, die Tage bleiben als Notizen erhalten. Gilt für dieses Gerät.
+                  </p>
+                </div>
+                <ToggleSwitch
+                  checked={journalOn}
+                  onChange={(v) => {
+                    setJournalEnabled(v);
+                    setJournalOn(v);
+                  }}
+                  title="Journal anzeigen"
+                />
+              </div>
+
               <div className="grid grid-cols-1 sm:grid-cols-2 gap-3">
                 {themes.map((t) => {
                   const isSelected = activeTheme === t.id;