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

openapi_first/templates/model_app/routes.py

@@ -1,5 +1,17 @@
 """
 CRUD route handlers bound via OpenAPI operationId.
+
+This module defines OpenAPI-bound operation handlers for a model-based
+CRUD service. Functions in this module are bound to HTTP routes
+exclusively via OpenAPI ``operationId`` values.
+
+Handlers explicitly control HTTP response status codes to ensure runtime
+behavior matches the OpenAPI contract. Domain models defined using
+Pydantic are used for request and response payloads.
+
+No routing decorators, path definitions, or implicit framework behavior
+appear in this module. All routing, HTTP methods, and schemas are defined
+in the OpenAPI specification.
 """
 
 from fastapi import Response, HTTPException
@@ -15,10 +27,42 @@ from data import (
 
 
 def list_items():
+    """
+    List all items.
+
+    Implements the OpenAPI operation identified by
+    ``operationId: list_items``.
+
+    Returns
+    -------
+    list[Item]
+        A list of item domain objects.
+    """
     return _list_items()
 
 
 def get_item(item_id: int):
+    """
+    Retrieve a single item by ID.
+
+    Implements the OpenAPI operation identified by
+    ``operationId: get_item``.
+
+    Parameters
+    ----------
+    item_id : int
+        Identifier of the item to retrieve.
+
+    Returns
+    -------
+    Item
+        The requested item.
+
+    Raises
+    ------
+    HTTPException
+        404 if the item does not exist.
+    """
     try:
         return _get_item(item_id)
     except KeyError:
@@ -26,12 +70,53 @@ def get_item(item_id: int):
 
 
 def create_item(payload: ItemCreate, response: Response):
+    """
+    Create a new item.
+
+    Implements the OpenAPI operation identified by
+    ``operationId: create_item``.
+
+    Parameters
+    ----------
+    payload : ItemCreate
+        Request body describing the item to create.
+    response : fastapi.Response
+        Response object used to set the HTTP status code.
+
+    Returns
+    -------
+    Item
+        The newly created item.
+    """
     item = _create_item(payload)
     response.status_code = 201
     return item
 
 
 def update_item(item_id: int, payload: ItemCreate):
+    """
+    Update an existing item.
+
+    Implements the OpenAPI operation identified by
+    ``operationId: update_item``.
+
+    Parameters
+    ----------
+    item_id : int
+        Identifier of the item to update.
+    payload : ItemCreate
+        New item data.
+
+    Returns
+    -------
+    Item
+        The updated item.
+
+    Raises
+    ------
+    HTTPException
+        404 if the item does not exist.
+    """
     try:
         return _update_item(item_id, payload)
     except KeyError:
@@ -39,6 +124,29 @@ def update_item(item_id: int, payload: ItemCreate):
 
 
 def delete_item(item_id: int, response: Response):
+    """
+    Delete an existing item.
+
+    Implements the OpenAPI operation identified by
+    ``operationId: delete_item``.
+
+    Parameters
+    ----------
+    item_id : int
+        Identifier of the item to delete.
+    response : fastapi.Response
+        Response object used to set the HTTP status code.
+
+    Returns
+    -------
+    None
+        No content.
+
+    Raises
+    ------
+    HTTPException
+        404 if the item does not exist.
+    """
     try:
         _delete_item(item_id)
     except KeyError: