docs(templates): document CRUD and model CRUD apps and expose them in mkdocs

- Add comprehensive module and function docstrings to crud_app and model_app templates
- Document OpenAPI-first guarantees, non-goals, and usage patterns in templates
- Add template-level __init__.py files with CLI and client usage examples
- Update mkdocs.yml to include CRUD and model-based CRUD template documentation
- Ensure template documentation follows strict package-bound mkdocstrings rules

docs/openapi_first/templates/crud_app/data.md

@@ -0,0 +1,3 @@
+# Data
+
+::: openapi_first.templates.crud_app.data