refactor(core): overhaul state transition architecture, persistent job queue, and API layer

- Implement atomic state transitions: add EntryService.PatchEntry() with EntryDiff computation and EventEntryTransition event emission.
- Add persistent SQLite task queue (JobEngine): add jobs table with crash recovery, exponential backoff retries, concurrency control, and idempotency key deduplication.
- Decompose monolithic HTTP handlers: split handlers.go into domain handlers (auth, feeds, entries, jobs, settings, rules, sse).
- Implement real-time Server-Sent Events (/api/events/stream) for multi-tab/device state synchronization.
- Fix SQLite concurrency: apply busy_timeout(10000) and journal_mode(WAL) via DSN query parameters to resolve SQLITE_BUSY (5).
- Fix AI settings & prompt loading: unmarshal JSON from ai_settings, apply configured prompt templates, and enforce strict enabled/API key validations.
- Fix undo share state: remove omitempty from ShareUUID to serialize null for state resets.
- Fix middle list counter: compute true unread/total stats from DB and clean switcher button labels.
- Adapt mobile UI for iOS: add viewport-fit=cover in index.html and calibrate safe-area insets for the bottom navigation and article reader toolbar.
- Add architectural documentation and worklog in docs/009_worklog.md.

web/src/styles/tokens.css

@@ -64,8 +64,9 @@
 
   /* Layout Dimensions */
   --header-height: 50px;
-  --bottom-nav-height: 72px;
-  --docked-audio-height: 56px;
+  --safe-area-bottom: env(safe-area-inset-bottom, 0px);
+  --bottom-nav-height: calc(50px + env(safe-area-inset-bottom, 0px));
+  --docked-audio-height: 54px;
   --sidebar-min-width: 200px;
   --sidebar-default-width: 250px;
   --list-min-width: 300px;