Add Popular tab to channel page

- YouTube sort=p fetch: indexes top 100 most-viewed videos from a channel,
  storing view_count in the DB
- Popular tab on channel page shows videos sorted by view_count DESC
- Videos/Popular tab switcher with context-appropriate fetch buttons
- Expose view_count in VideoOut; add 'popular' sort to channel videos endpoint

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

backend/routers/channels.py

@@ -62,6 +62,7 @@ class VideoOut(BaseModel):
     is_downloaded: bool = False
     is_watched: bool = False
     queued: bool = False
+    view_count: Optional[int] = None
 
     model_config = {"from_attributes": True}
 
@@ -608,10 +609,11 @@ def get_channel_videos(
 ):
     _get_channel_or_404(db, channel_id)
     order = {
-        "newest": "v.published_at DESC NULLS LAST",
-        "oldest": "v.published_at ASC NULLS LAST",
-        "title": "v.title ASC",
-        "unwatched": "COALESCE(uv.watched, 0) ASC, v.published_at DESC NULLS LAST",
+        "newest":   "v.published_at DESC NULLS LAST",
+        "oldest":   "v.published_at ASC NULLS LAST",
+        "title":    "v.title ASC",
+        "unwatched":"COALESCE(uv.watched, 0) ASC, v.published_at DESC NULLS LAST",
+        "popular":  "v.view_count DESC NULLS LAST",
     }.get(sort, "v.published_at DESC NULLS LAST")
     params: dict = {"user_id": current_user.id, "channel_id": channel_id, "limit": limit, "offset": offset}
     q_clause = ""
@@ -621,7 +623,7 @@ def get_channel_videos(
     rows = db.execute(
         text(f"""
             SELECT v.id, v.youtube_video_id, v.title, v.thumbnail_url,
-                   v.duration_seconds, v.published_at,
+                   v.duration_seconds, v.published_at, v.view_count,
                    COALESCE(uv.downloaded, 0) AS is_downloaded,
                    COALESCE(uv.watched, 0) AS is_watched
             FROM videos v
@@ -635,6 +637,77 @@ def get_channel_videos(
     return [VideoOut(**dict(r)) for r in rows]
 
 
+@router.post("/{channel_id}/fetch-popular", status_code=status.HTTP_202_ACCEPTED)
+def fetch_popular_videos(
+    channel_id: int,
+    background_tasks: BackgroundTasks,
+    db: Session = Depends(get_db),
+    current_user: User = Depends(get_current_user),
+):
+    """Fetch the channel's most popular videos from YouTube and index them."""
+    channel = _get_channel_or_404(db, channel_id)
+    background_tasks.add_task(_fetch_popular_task, channel_id, channel.youtube_channel_id)
+    return {"detail": "Fetching popular videos"}
+
+
+def _fetch_popular_task(channel_id: int, youtube_channel_id: str):
+    from ..database import SessionLocal
+    db = SessionLocal()
+    try:
+        if youtube_channel_id.startswith("@"):
+            url = f"https://www.youtube.com/{youtube_channel_id}/videos?sort=p"
+        else:
+            url = f"https://www.youtube.com/channel/{youtube_channel_id}/videos?sort=p"
+
+        stdout, _, code = ytdlp._run([
+            "yt-dlp", url,
+            "--dump-json", "--flat-playlist",
+            "--playlist-end", "100",
+            "--quiet",
+            *ytdlp._cookie_args(),
+        ], timeout=120)
+
+        channel = db.query(Channel).filter_by(id=channel_id).first()
+        if not channel:
+            return
+
+        for line in stdout.splitlines():
+            line = line.strip()
+            if not line:
+                continue
+            try:
+                info = json.loads(line)
+            except json.JSONDecodeError:
+                continue
+            yt_id = info.get("id")
+            if not yt_id:
+                continue
+            existing = db.query(Video).filter_by(youtube_video_id=yt_id).first()
+            view_count = info.get("view_count")
+            published_at = ytdlp._parse_published(info)
+            if existing:
+                if view_count is not None:
+                    existing.view_count = view_count
+                if published_at and not existing.published_at:
+                    existing.published_at = published_at
+            else:
+                db.add(Video(
+                    youtube_video_id=yt_id,
+                    channel_id=channel.id,
+                    title=info.get("title", ""),
+                    thumbnail_url=ytdlp._stable_thumbnail(yt_id),
+                    duration_seconds=info.get("duration"),
+                    published_at=published_at,
+                    tags=json.dumps(info.get("tags") or []),
+                    view_count=view_count,
+                ))
+        db.commit()
+    except Exception:
+        db.rollback()
+    finally:
+        db.close()
+
+
 @router.post("/{channel_id}/search", status_code=status.HTTP_202_ACCEPTED)
 def search_channel_youtube(
     channel_id: int,