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.

.containerignore

@@ -0,0 +1,38 @@
+# Git
+.git
+.gitignore
+
+# Python
+__pycache__
+*.py[cod]
+*$py.class
+*.so
+.Python
+.venv
+.env
+*.egg-info
+dist
+build
+
+# Testing
+.pytest_cache
+.coverage
+htmlcov
+.tox
+.mypy_cache
+.ruff_cache
+
+# IDE
+.idea
+.vscode
+*.swp
+*.swo
+
+# Project specific
+data/
+*.db
+.claude
+docs/
+tests/
+*.md
+.pre-commit-config.yaml