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.

internal/events/bus.go

@@ -12,15 +12,24 @@ import (
 type EventType string
 
 const (
-	EventPostCreated    EventType = "on_post_created"
-	EventPostUpdated    EventType = "on_post_updated"
-	EventVariantUpdated EventType = "on_variant_updated"
-	EventManualTrigger  EventType = "manual"
+	EventPostCreated     EventType = "on_post_created"
+	EventPostUpdated     EventType = "on_post_updated"
+	EventVariantUpdated  EventType = "on_variant_updated"
+	EventEntryTransition EventType = "on_entry_transition"
+	EventManualTrigger   EventType = "manual"
+	EventJobProgress     EventType = "job_progress"
+	EventJobCompleted    EventType = "job_completed"
+	EventJobFailed       EventType = "job_failed"
+	EventPreferencesSync EventType = "preferences_updated"
 )
 
 type Event struct {
 	Type        EventType
 	Entry       models.FeedEntry
+	OldEntry    *models.FeedEntry
+	NewEntry    *models.FeedEntry
+	Diff        *models.EntryDiff
+	Job         *models.Job
 	VariantKey  string // populated when Type == EventVariantUpdated
 	Depth       int
 	DirectAttrs map[string]interface{}