Containerize backend with Docker Compose

Added Docker support for easy deployment:
- Dockerfile: Python 3.11 slim image with FastAPI app
- docker-compose.yml: Service definition with volume mounting for data persistence
- .dockerignore: Exclude unnecessary files from Docker build
- database.py: Updated to store SQLite DB in ./data directory for volume persistence
- .gitignore: Added entries for database files and data directory
- README.md: Comprehensive documentation with Docker and local setup instructions

The application can now be run with: docker compose up -d
Database persists in ./data directory mounted as a volume

.dockerignore

@@ -0,0 +1,19 @@
+__pycache__
+*.pyc
+*.pyo
+*.pyd
+.Python
+*.so
+*.egg
+*.egg-info
+dist
+build
+.git
+.gitignore
+*.db
+*.db-journal
+.env
+.venv
+venv/
+ENV/
+data/