docs: Add comprehensive documentation to recipe generator
Add detailed docstrings and inline comments to all recipe generator modules explaining classes, functions, and complex logic in plain English.
Files updated:
- recipe-generator/recipe_generator.py: Module, class, and method docs
- recipe-generator/cli.py: CLI modes, arguments, and workflow docs
- recipe-generator/validators.py: Three-layer validation architecture docs
- recipe-generator/manifest.py: Manifest processing and variant expansion docs
- recipe-generator/generate_recipe.py: Entry point documentation