perf(recents): batch Xtream remove-recent-item into a single IPC call

Clearing all recents of a given content type fired N concurrent IPC calls,
each opening its own implicit transaction in the recently_viewed table.
For users with hundreds of recently-watched VOD/series rows this added
real overhead even though the UI updates optimistically.

Add a new DB_REMOVE_RECENT_ITEMS_BATCH path end-to-end:
- removeRecentItemsBatch() Drizzle op: one transaction, one prepared
  statement reused per row
- Wire through worker → IPC handler → preload → window.electron typings
  → DatabaseService
- UnifiedRecentDataService.removeRecentItemsBatch() groups items by
  source. Xtream items go through the new batch IPC. M3U/Stalker items
  still go per-playlist because they update a JSON column on the
  playlist row, not the recently_viewed table — but they now run in
  parallel with the Xtream batch via a single Promise.all.
- Single call site updated: unified-collection-page "Clear all of type"
  confirmation handler.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>
Entire-Checkpoint: 4bfb62f988b7

apps/electron-backend/src/app/api/main.preload.ts

@@ -540,6 +540,9 @@ const electronApi = {
         ipcRenderer.invoke('DB_CLEAR_PLAYLIST_RECENT_ITEMS', playlistId),
     dbRemoveRecentItem: (contentId: number, playlistId: string) =>
         ipcRenderer.invoke('DB_REMOVE_RECENT_ITEM', contentId, playlistId),
+    dbRemoveRecentItemsBatch: (
+        items: { contentId: number; playlistId: string }[]
+    ) => ipcRenderer.invoke('DB_REMOVE_RECENT_ITEMS_BATCH', items),
     dbGetContentByXtreamId: (
         xtreamId: number,
         playlistId: string,