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.

.gitignore

@@ -0,0 +1,6 @@
+__pycache__/
+*.pyc
+*.db
+.env
+venv/
+.pytest_cache/