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/main.py

@@ -1,13 +1,23 @@
 import asyncio
+import logging
 from contextlib import asynccontextmanager
 from datetime import datetime
-from fastapi import FastAPI
+from fastapi import FastAPI, Request
 from fastapi.middleware.cors import CORSMiddleware
 from sqlalchemy import select
 from .routers import auth, rooms, tracks, websocket, messages
 from .database import async_session
 from .models.room import Room
 from .services.sync import manager
+from .config import get_settings
+
+# Setup logging
+logging.basicConfig(level=logging.INFO)
+logger = logging.getLogger(__name__)
+
+# Log config on startup
+settings = get_settings()
+logger.info(f"DATABASE_URL: {settings.database_url}")
 
 
 async def periodic_sync():
@@ -65,6 +75,15 @@ async def lifespan(app: FastAPI):
 
 app = FastAPI(title="EnigFM", description="Listen to music together with friends", lifespan=lifespan)
 
+
+@app.middleware("http")
+async def log_requests(request: Request, call_next):
+    logger.info(f"Request: {request.method} {request.url.path}")
+    response = await call_next(request)
+    logger.info(f"Response: {request.method} {request.url.path} - {response.status_code}")
+    return response
+
+
 # CORS
 app.add_middleware(
     CORSMiddleware,