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/lib/api.ts

@@ -4,6 +4,7 @@ import {
   DashboardStats,
   Document,
   TrashedDocument,
+  JournalDay,
   BackupFile,
   DataSection,
   ApiKeyScope,
@@ -723,6 +724,17 @@ export const api = {
     return request<TrashedDocument[]>('/api/v1/documents/trash');
   },
 
+  /** Days of the own journal (newest first) with their notes. */
+  async getJournal(): Promise<JournalDay[]> {
+    const res = await request<{ days: JournalDay[] }>('/api/v1/journal');
+    return res.days || [];
+  },
+
+  /** The note of a journal day (YYYY-MM-DD); created on first use. */
+  async openJournalDay(date: string): Promise<Document> {
+    return request<Document>(`/api/v1/journal/${date}`, { method: 'POST' });
+  },
+
   /** Creates a note from a bullet's children; the editor then replaces the branch by `link` itself. */
   async extractBranch(docId: string, blockId: string, clientId: string): Promise<{ document: Document; link: string }> {
     return request<{ document: Document; link: string }>(`/api/v1/documents/${docId}/extract`, {