feat: add containerization support

- Add Containerfile with multi-stage build for minimal image
- Add .containerignore to exclude unnecessary files
- Add /health endpoint for container health checks
- Update main.py to expose Flask app for gunicorn

Uses Python 3.12-slim base, runs as non-root user, exposes port 8000.

main.py

@@ -1,6 +1,14 @@
-def main():
-    print("Hello from sneaky-klaus!")
+"""Application entry point for Sneaky Klaus.
 
+This module creates the Flask application instance for use with
+gunicorn or the Flask development server.
+"""
+
+from src.app import create_app
+
+# Create app instance for gunicorn (production)
+app = create_app()
 
 if __name__ == "__main__":
-    main()
+    # Development server
+    app.run(host="0.0.0.0", port=5000, debug=True)