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/database/operations/recently-viewed.operations.ts

@@ -150,3 +150,36 @@ export async function removeRecentItem(
 
     return { success: true };
 }
+
+export async function removeRecentItemsBatch(
+    db: AppDatabase,
+    items: { contentId: number; playlistId: string }[]
+): Promise<{ success: boolean; count: number }> {
+    if (!Array.isArray(items) || items.length === 0) {
+        return { success: true, count: 0 };
+    }
+
+    const stmt = db
+        .delete(schema.recentlyViewed)
+        .where(
+            and(
+                eq(
+                    schema.recentlyViewed.contentId,
+                    sql.placeholder('contentId')
+                ),
+                eq(
+                    schema.recentlyViewed.playlistId,
+                    sql.placeholder('playlistId')
+                )
+            )
+        )
+        .prepare();
+
+    await db.transaction(async () => {
+        for (const { contentId, playlistId } of items) {
+            await stmt.execute({ contentId, playlistId });
+        }
+    });
+
+    return { success: true, count: items.length };
+}