fix: ReccoBeats audio features and OpenAI narrative generation

- Add reccobeats_id column to Track model for API mapping
- Fix ReccoBeats batch size limit (max 40 IDs per request)
- Extract spotify_id from href field in ReccoBeats responses
- Fix OpenAI API: remove unsupported temperature param, increase max_completion_tokens to 4000
- Add playlist/user management methods to spotify_client for future auto-playlist feature

backend/app/models.py

@@ -39,6 +39,7 @@ class Track(Base):
     __tablename__ = "tracks"
 
     id = Column(String, primary_key=True, index=True)  # Spotify ID
+    reccobeats_id = Column(String, nullable=True, index=True)  # ReccoBeats UUID
     name = Column(String)
     artist = Column(
         String