Add started_count to stats (videos in progress, not yet finished)

Tracks watch_progress_seconds > 0 AND watched = 0. Shown as
"In progress" card in the engagement row alongside finished/bailed/rewatched.
Total liked moved to engagement row, top row condensed to 3 cards.

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

backend/routers/stats.py

@@ -136,6 +136,15 @@ def get_stats(
         {"uid": uid},
     ).mappings().first()
 
+    started_count = db.execute(
+        text("""
+            SELECT COUNT(*) AS n FROM user_videos
+            WHERE user_id = :uid AND watched = 0
+              AND watch_progress_seconds > 0
+        """),
+        {"uid": uid},
+    ).mappings().first()
+
     try:
         disk = shutil.disk_usage(settings.download_path)
         download_bytes = sum(
@@ -164,6 +173,7 @@ def get_stats(
         "total_rewatches": avg_completion["total_rewatches"] or 0,
         "rewatched_videos": avg_completion["rewatched_videos"] or 0,
         "total_liked": liked_count["n"] or 0,
+        "started_count": started_count["n"] or 0,
         "top_categories": [dict(r) for r in top_categories],
         "peak_hours": [dict(r) for r in peak_hours],
         "taste_profile": [dict(r) for r in taste_profile],