feat: migrate to PostgreSQL and enhance playlist curation

- Migrate database from SQLite to PostgreSQL (100.91.248.114:5433)
- Fix playlist curation to use actual top tracks instead of AI name matching
- Add /playlists/history endpoint for historical playlist viewing
- Add Playlist Archives section to frontend with expandable history
- Add playlist-modify-* scopes to Spotify OAuth for playlist creation
- Rewrite Genius client to use official API (fixes 403 scraping blocks)
- Ensure playlists are created on Spotify before curation attempts
- Add DATABASE.md documentation for PostgreSQL schema
- Add migrations for PlaylistConfig and composition storage

backend/app/services/spotify_client.py

@@ -71,6 +71,26 @@ class SpotifyClient:
                 return None
             return response.json()
 
+    async def get_tracks(self, track_ids: List[str]) -> List[Dict[str, Any]]:
+        """Fetch multiple tracks by ID."""
+        if not track_ids:
+            return []
+
+        token = await self.get_access_token()
+        ids_param = ",".join(track_ids[:50])
+
+        async with httpx.AsyncClient() as client:
+            response = await client.get(
+                f"{SPOTIFY_API_BASE}/tracks",
+                params={"ids": ids_param},
+                headers={"Authorization": f"Bearer {token}"},
+            )
+            if response.status_code != 200:
+                print(f"Error fetching tracks: {response.text}")
+                return []
+
+            return response.json().get("tracks", [])
+
     async def get_artists(self, artist_ids: List[str]) -> List[Dict[str, Any]]:
         """
         Fetches artist details (including genres) for a list of artist IDs.