feat: persistent photo job queue, worker, history with rollback

- Replace in-memory photoAiJobs Map with DB-backed photo_jobs table
- Background photo worker (worker.js) with retry, backoff, stale reset
  - Handles both AI (Real-ESRGAN) and server-side (sharp) enhancement
  - Controlled via photo_worker_enabled setting
- Photo job history in enhance modal with before/after thumbnails + rollback
- Worker dashboard: photo jobs section with status counts, recent table,
  compare slider for before/after, rollback from worker UI
- New endpoints: /api/photo-jobs/status|wake|enabled|requeue-failed,
  /api/entries/:id/photo/jobs (history), .../rollback
- swapEntryPhotoFiles logs every mutation to photo_jobs table

db/migration.sql

@@ -200,4 +200,24 @@ DROP TRIGGER IF EXISTS trg_entries_notify ON entries;
 CREATE TRIGGER trg_entries_notify AFTER INSERT OR UPDATE OF ai_status ON entries
 FOR EACH ROW EXECUTE FUNCTION notify_entries_changed();
 
+CREATE TABLE IF NOT EXISTS photo_jobs (
+  id SERIAL PRIMARY KEY,
+  entry_id INT NOT NULL REFERENCES entries(id) ON DELETE CASCADE,
+  action VARCHAR(20) NOT NULL DEFAULT 'ai',
+  params JSONB,
+  before_path VARCHAR(255),
+  after_path VARCHAR(255),
+  status VARCHAR(20) NOT NULL DEFAULT 'pending',
+  attempts INT NOT NULL DEFAULT 0,
+  error TEXT,
+  created_at TIMESTAMPTZ DEFAULT now(),
+  finished_at TIMESTAMPTZ
+);
+
+CREATE INDEX IF NOT EXISTS idx_photo_jobs_pending ON photo_jobs(id) WHERE status = 'pending';
+CREATE INDEX IF NOT EXISTS idx_photo_jobs_entry_id ON photo_jobs(entry_id);
+
+INSERT INTO settings (key, value) VALUES ('photo_worker_enabled', 'true')
+ON CONFLICT (key) DO NOTHING;
+
 ALTER TABLE entries ADD COLUMN IF NOT EXISTS photo_original_path VARCHAR(255);