fix: feedback round 2 — language, subscriptions, feed scope, UX

- Language detection: classify one cleaned+concatenated blob (strip emoji,
  @mentions, #tags, numbers, punctuation); fixes caps/emoji-heavy channels
  (e.g. Nessaj -> Hungarian, no more bogus Chinese/Korean)
- Feed now joins the user's subscriptions, so unsubscribing on YouTube removes a
  channel from the feed; periodic subscription re-sync job picks up changes
- Watched/Saved/Hidden views ignore the Shorts/live default-hiding so the full
  set is visible (fixes hidden videos missing from the Hidden view)
- Persist feed filters + search across reloads (localStorage)
- 3D polish: cards lift with shadow on hover; chips/buttons get depth and a
  press effect; undo toast lasts longer

backend/app/scheduler.py

@@ -13,6 +13,7 @@ from app.sync.runner import (
     run_recent_backfill,
     run_rss_poll,
     run_shorts,
+    run_subscription_resync,
 )
 
 logger = logging.getLogger("subfeed.scheduler")
@@ -58,6 +59,10 @@ def _shorts_job() -> None:
     _job("shorts", run_shorts)
 
 
+def _subscriptions_job() -> None:
+    _job("subscriptions", run_subscription_resync)
+
+
 def start_scheduler() -> None:
     global _scheduler
     if not settings.scheduler_enabled or _scheduler is not None:
@@ -87,6 +92,12 @@ def start_scheduler() -> None:
         minutes=settings.shorts_probe_interval_minutes,
         id="shorts",
     )
+    scheduler.add_job(
+        _subscriptions_job,
+        "interval",
+        minutes=settings.subscriptions_resync_minutes,
+        id="subscriptions",
+    )
     scheduler.start()
     _scheduler = scheduler
     logger.info("scheduler started")