Implement Phase 2 Frontend and Phase 3 Data Enrichment

- Initialize React+Vite Frontend with Ant Design Dashboard.
- Implement Data Enrichment: ReccoBeats (Audio Features) and Spotify (Genres).
- Update Database Schema via Alembic Migrations.
- Add Docker support (Dockerfile, docker-compose.yml).
- Update README with hosting instructions.

backend/app/services/reccobeats_client.py

@@ -0,0 +1,18 @@
+import httpx
+from typing import List, Dict, Any
+
+RECCOBEATS_API_URL = "https://api.reccobeats.com/v1/audio-features"
+
+class ReccoBeatsClient:
+    async def get_audio_features(self, spotify_ids: List[str]) -> List[Dict[str, Any]]:
+        if not spotify_ids:
+            return []
+        ids_param = ",".join(spotify_ids)
+        async with httpx.AsyncClient() as client:
+            try:
+                response = await client.get(RECCOBEATS_API_URL, params={"ids": ids_param})
+                if response.status_code != 200:
+                    return []
+                return response.json().get("content", [])
+            except Exception:
+                return []