feat(header): clarify video counts and hide idle pause button

Show 'N yours / M total' in the header (your subscriptions vs. the whole shared
catalog) with a tooltip, backed by a new total_videos field on /sync/my-status.
The admin pause button now only appears when there's sync work to pause; Resume
still shows whenever sync is paused.

frontend/src/lib/api.ts

@@ -173,6 +173,7 @@ export interface MyStatus {
   deep_pending_count: number;
   deep_eta_seconds: number;
   my_videos: number;
+  total_videos: number;
   quota_used_today: number;
   quota_remaining_today: number;
   paused: boolean;