Add track filtering, WS keepalive, and improve error handling

- Add track filtering by uploader (my tracks / all tracks) with UI tabs
- Add WebSocket ping/pong keepalive (30s interval) to prevent disconnects
- Add auto-reconnect on WebSocket close (3s delay)
- Add request logging middleware with DATABASE_URL output on startup
- Handle missing S3 files gracefully (return 404 instead of 500)
- Add debug logging for audio ended event

🤖 Generated with [Claude Code](https://claude.com/claude-code)

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

backend/app/routers/tracks.py

@@ -19,8 +19,16 @@ router = APIRouter(prefix="/api/tracks", tags=["tracks"])
 
 
 @router.get("", response_model=list[TrackResponse])
-async def get_tracks(db: AsyncSession = Depends(get_db)):
-    result = await db.execute(select(Track).order_by(Track.created_at.desc()))
+async def get_tracks(
+    my: bool = False,
+    db: AsyncSession = Depends(get_db),
+    current_user: User = Depends(get_current_user)
+):
+    query = select(Track)
+    if my:
+        query = query.where(Track.uploaded_by == current_user.id)
+    query = query.order_by(Track.created_at.desc())
+    result = await db.execute(query)
     return result.scalars().all()
 
 
@@ -174,6 +182,8 @@ async def stream_track(track_id: uuid.UUID, request: Request, db: AsyncSession =
 
     # Get file size from S3 (without downloading)
     file_size = get_file_size(track.s3_key)
+    if file_size is None:
+        raise HTTPException(status_code=status.HTTP_404_NOT_FOUND, detail="Track file not found in storage")
 
     # Encode filename for non-ASCII characters
     encoded_filename = quote(f"{track.title}.mp3")