perf(workspace): share the startup inventory read and defer non-first-card IPC (J1)

Journey J1 / renderer.ipcCallsToFirstCard: 12 -> 7.

- PlaylistsService.getAllPlaylists() shares one in-flight SQLite read
  between concurrent callers (the playlist effect and the XMLTV source
  reconciliation at startup). Settled reads are never reused and every
  SQLite write detaches the pending read.
- getM3uFavoriteChannels() stops re-reading the write-once IndexedDB ->
  SQLite migration receipt once it has been seen.
- StartupDeferralService holds the download list, app update status and
  the dashboard's recent items and favorites until one task after the
  render that reveals the routed content (5 s safety timeout).
  IPTVNATOR_DISABLE_STARTUP_DEFERRAL=1 is the kill switch.
- reconcileEpgSources and the two distinct migration-flag reads stay on
  the critical path: the first is the #1548 revision fence, the second
  are different keys, not duplicates.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

libs/shared/interfaces/src/lib/electron-api.interface.ts

@@ -710,6 +710,11 @@ export interface ElectronBridgeApi {
     ) => () => void;
     getAppVersion: () => Promise<string>;
     platform: string;
+    /**
+     * `IPTVNATOR_DISABLE_STARTUP_DEFERRAL=1` kill switch: issue deferred
+     * startup work immediately instead of after the first rendered screen.
+     */
+    startupDeferralDisabled?: boolean;
     getAppUpdateStatus: () => Promise<ElectronBridgeAppUpdateStatus>;
     checkForAppUpdate: () => Promise<ElectronBridgeAppUpdateStatus>;
     downloadAppUpdate: () => Promise<ElectronBridgeAppUpdateStatus>;