ci: Add DevOps quality assurance with pre-commit hooks and GitHub Actions

- Add pre-commit hooks: Ruff lint/format, Bandit security scan, YAML/TOML validation
- Add GitHub Actions CI workflow: lint, security, test, and build jobs
- Configure Ruff and Bandit in pyproject.toml
- Add pytest test suite for build_epub.py (25 tests)
- Fix code issues: exception chaining, httpx timeout, formatting
- Add requirements.txt and requirements-dev.txt

.gitignore

@@ -48,4 +48,18 @@ yarn-error.log*
 blog-posts/
 
 # EPUB files in root directory
-/*.epub
+/*.epub
+
+# Python virtual environment
+.venv/
+
+# Python cache
+__pycache__/
+*.py[cod]
+*$py.class
+*.so
+.pytest_cache/
+.mypy_cache/
+*.egg-info/
+dist/
+build/