chore: update Docker configuration and improve health check functionality

- Added Docker health check endpoint to the FastAPI application, returning a 200 status when the app is running.
- Updated Dockerfile to include curl for health checks and modified entrypoint script to exit on errors.
- Enhanced .dockerignore and .gitignore files to exclude coverage and test artifacts.
- Updated docker-compose.prod.yml to specify version.
- Added pytest-cov as a development dependency to improve test coverage reporting.

duty_teller/api/app.py

@@ -35,6 +35,14 @@ def _is_valid_calendar_token(token: str) -> bool:
 
 
 app = FastAPI(title="Duty Teller API")
+
+
+@app.get("/health", summary="Health check")
+def health() -> dict:
+    """Return 200 when the app is up. Used by Docker HEALTHCHECK."""
+    return {"status": "ok"}
+
+
 app.add_middleware(
     CORSMiddleware,
     allow_origins=config.CORS_ORIGINS,