feat: import review step + admin notifications

- Import page: add file upload with review step before committing
- Backend: add analyze endpoint to preview chapters before import
- Add notifications collection + API for admin alerts
- Add bell icon in header with notification dropdown (admin only)
- Runner creates notification on import completion
- Notifications link to /admin/import for easy review

backend/cmd/runner/main.go

@@ -203,6 +203,7 @@ func run() error {
 		PocketTTS:        pocketTTSClient,
 		CFAI:             cfaiClient,
 		LibreTranslate:   ltClient,
+		Notifier:         store,
 		Log:              log,
 	}
 	r := runner.New(rCfg, deps)