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/crud_app/data.py

@@ -3,27 +3,88 @@ In-memory mock data store for CRUD example.
 
 This module intentionally avoids persistence and concurrency guarantees.
 It is suitable for demos, tests, and scaffolding only.
+
+It intentionally avoids
+- persistence
+- concurrency guarantees
+- validation
+- error handling
+
+The implementation is suitable for:
+- demonstrations
+- tests
+- scaffolding and example services
+
+It is explicitly NOT suitable for production use.
+
+This module is not part of the ``openapi_first`` library API surface.
 """
 
 from typing import Dict
 
+
+# In-memory storage keyed by item ID.
 _items: Dict[int, dict] = {
     1: {"id": 1, "name": "Apple", "price": 0.5},
     2: {"id": 2, "name": "Banana", "price": 0.3},
 }
 
+# Auto-incrementing ID counter.
 _next_id = 3
 
 
 def list_items():
+    """
+    Return all items in the data store.
+
+    This function performs no filtering, pagination, or sorting.
+    The returned collection reflects the current in-memory state.
+
+    Returns
+    -------
+    list[dict]
+        A list of item representations.
+    """
     return list(_items.values())
 
 
 def get_item(item_id: int):
+    """
+    Retrieve a single item by ID.
+
+    This function assumes the item exists and will raise ``KeyError``
+    if the ID is not present in the store.
+
+    Parameters
+    ----------
+    item_id : int
+        Identifier of the item to retrieve.
+
+    Returns
+    -------
+    dict
+        The stored item representation.
+    """
     return _items[item_id]
 
 
 def create_item(payload: dict):
+    """
+    Create a new item in the data store.
+
+    A new integer ID is assigned automatically. No validation is
+    performed on the provided payload.
+
+    Parameters
+    ----------
+    payload : dict
+        Item attributes excluding the ``id`` field.
+
+    Returns
+    -------
+    dict
+        The newly created item, including its assigned ID.
+    """
     global _next_id
     item = {"id": _next_id, **payload}
     _items[_next_id] = item
@@ -32,10 +93,40 @@ def create_item(payload: dict):
 
 
 def update_item(item_id: int, payload: dict):
+    """
+    Replace an existing item in the data store.
+
+    This function overwrites the existing item entirely and does not
+    perform partial updates or validation. If the item does not exist,
+    it will be created implicitly.
+
+    Parameters
+    ----------
+    item_id : int
+        Identifier of the item to update.
+    payload : dict
+        Item attributes excluding the ``id`` field.
+
+    Returns
+    -------
+    dict
+        The updated item representation.
+    """
     item = {"id": item_id, **payload}
     _items[item_id] = item
     return item
 
 
 def delete_item(item_id: int):
+    """
+    Remove an item from the data store.
+
+    This function assumes the item exists and will raise ``KeyError``
+    if the ID is not present.
+
+    Parameters
+    ----------
+    item_id : int
+        Identifier of the item to delete.
+    """
     del _items[item_id]