Auto-schedule daily discovery + fix Find More UX + expand query diversity

Auto-discovery daemon:
- Runs every hour, triggers full discovery for any user whose last run
  was >23 hours ago. First check is 5 minutes after startup.
- Tracks run time in user_settings.last_discovery_run (new column).
- Manual Find More also stamps last_discovery_run.

Discovery status endpoint (GET /api/discovery/status):
- Returns pending_count (unseen queue size) and last_run timestamp.
- Shown in the Discover page header so users know queue state at a glance.

Find More UX fix:
- Was: kick background task, wait 8 seconds, refetch (task takes minutes).
- Now: button shows "Queued ✓" on success with an explanatory banner
  telling the user it takes a few minutes and also runs daily automatically.

Query diversity:
- Added "best [category] channels" serendipity queries to crawl_by_search.
- Limit raised from 25 to 30 queries per run.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

backend/main.py

@@ -131,6 +131,7 @@ def on_startup():
             created_at DATETIME DEFAULT CURRENT_TIMESTAMP
         )""",
         "ALTER TABLE user_videos ADD COLUMN feed_shown_count INTEGER NOT NULL DEFAULT 0",
+        "ALTER TABLE user_settings ADD COLUMN last_discovery_run DATETIME DEFAULT NULL",
     ]:
         try:
             db.execute(text(col_sql))
@@ -217,6 +218,48 @@ def on_startup():
 
     threading.Thread(target=_auto_sync_daemon, daemon=True).start()
 
+    def _auto_discovery_daemon():
+        import time as _time
+        from datetime import datetime as _dt, timedelta as _td
+        from sqlalchemy import text as _text
+        from .services.discovery import run_full_discovery
+
+        # Wait 5 minutes after startup before the first check so the app can
+        # finish initialising and existing enrichment tasks can settle.
+        _time.sleep(300)
+
+        while True:
+            try:
+                db = SessionLocal()
+                try:
+                    rows = db.execute(_text("""
+                        SELECT u.id AS user_id,
+                               COALESCE(us.discovery_regions, 'US,SE') AS discovery_regions,
+                               us.last_discovery_run
+                        FROM users u
+                        LEFT JOIN user_settings us ON u.id = us.user_id
+                    """)).mappings().all()
+
+                    for row in rows:
+                        last = row["last_discovery_run"]
+                        if last is None or (_dt.utcnow() - _dt.fromisoformat(str(last))) > _td(hours=23):
+                            uid = row["user_id"]
+                            regions = [r.strip().upper() for r in (row["discovery_regions"] or "US,SE").split(",") if r.strip()]
+                            run_full_discovery(db, uid, regions)
+                            db.execute(
+                                _text("UPDATE user_settings SET last_discovery_run = :now WHERE user_id = :uid"),
+                                {"now": _dt.utcnow(), "uid": uid},
+                            )
+                            db.commit()
+                finally:
+                    db.close()
+            except Exception:
+                pass
+
+            _time.sleep(3600)  # check every hour, run if >23 h since last run
+
+    threading.Thread(target=_auto_discovery_daemon, daemon=True).start()
+
 
 @app.get("/api/health")
 def health():