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

database.py

@@ -1,8 +1,12 @@
 from sqlalchemy import create_engine
 from sqlalchemy.ext.declarative import declarative_base
 from sqlalchemy.orm import sessionmaker
+import os
 
-SQLALCHEMY_DATABASE_URL = "sqlite:///./seismo_fleet.db"
+# Ensure data directory exists
+os.makedirs("data", exist_ok=True)
+
+SQLALCHEMY_DATABASE_URL = "sqlite:///./data/seismo_fleet.db"
 
 engine = create_engine(
     SQLALCHEMY_DATABASE_URL, connect_args={"check_same_thread": False}