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

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+# Data
+
+::: openapi_first.templates.crud_app.data

docs/openapi_first/templates/crud_app/index.md

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+# Crud App
+
+::: openapi_first.templates.crud_app

docs/openapi_first/templates/crud_app/main.md

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+# Main
+
+::: openapi_first.templates.crud_app.main

docs/openapi_first/templates/crud_app/routes.md

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+# Routes
+
+::: openapi_first.templates.crud_app.routes

docs/openapi_first/templates/crud_app/test_crud_app.md

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+# Test Crud App
+
+::: openapi_first.templates.crud_app.test_crud_app