feat: Initial backend setup for Music Analyser

- Created FastAPI backend structure.
- Implemented Spotify Recently Played ingestion logic.
- Set up SQLite database with SQLAlchemy models.
- Added AI Service using Google Gemini.
- Created helper scripts for auth and background worker.
- Added Dockerfile and GitHub Actions workflow.

backend/requirements.txt

@@ -0,0 +1,11 @@
+fastapi==0.109.2
+uvicorn==0.27.1
+sqlalchemy==2.0.27
+httpx==0.26.0
+python-dotenv==1.0.1
+pydantic==2.6.1
+pydantic-settings==2.1.0
+google-generativeai==0.3.2
+tenacity==8.2.3
+python-dateutil==2.9.0.post0
+requests==2.31.0