feat(scaffold): add model-backed CRUD service template

Provides a complete OpenAPI-first CRUD example with a Pydantic
model layer, explicit runtime semantics, and integration tests
to support developer onboarding and real-world service structure.

openapi_first/templates/model_app/test_model_app.py

@@ -0,0 +1,98 @@
+"""
+End-to-end tests for the OpenAPI-first model CRUD example app.
+
+These tests validate that all CRUD operations behave correctly
+against the in-memory mock data store using Pydantic models.
+
+The tests assume:
+- OpenAPI-first route binding
+- Pydantic model validation
+- In-memory storage (no persistence guarantees)
+- Deterministic behavior in a single process
+"""
+
+from fastapi.testclient import TestClient
+
+from main import app
+
+
+client = TestClient(app)
+
+
+def test_list_items_initial():
+    """Initial items should be present."""
+    response = client.get("/items")
+    assert response.status_code == 200
+
+    data = response.json()
+    assert isinstance(data, list)
+    assert len(data) >= 2
+
+    ids = {item["id"] for item in data}
+    assert 1 in ids
+    assert 2 in ids
+
+
+def test_get_item():
+    """Existing item should be retrievable by ID."""
+    response = client.get("/items/1")
+    assert response.status_code == 200
+
+    item = response.json()
+    assert item["id"] == 1
+    assert isinstance(item["name"], str)
+    assert isinstance(item["price"], float)
+
+
+def test_create_item():
+    """Creating a new item should return the created entity."""
+    payload = {
+        "name": "Orange",
+        "price": 0.8,
+    }
+
+    response = client.post("/items", json=payload)
+    assert response.status_code == 201
+
+    item = response.json()
+    assert "id" in item
+    assert item["name"] == payload["name"]
+    assert item["price"] == payload["price"]
+
+    # Verify it appears in list
+    list_response = client.get("/items")
+    ids = {i["id"] for i in list_response.json()}
+    assert item["id"] in ids
+
+
+def test_update_item():
+    """Updating an item should replace its values."""
+    payload = {
+        "name": "Green Apple",
+        "price": 0.6,
+    }
+
+    response = client.put("/items/1", json=payload)
+    assert response.status_code == 200
+
+    item = response.json()
+    assert item["id"] == 1
+    assert item["name"] == payload["name"]
+    assert item["price"] == payload["price"]
+
+    # Verify persisted update
+    get_response = client.get("/items/1")
+    updated = get_response.json()
+    assert updated["name"] == payload["name"]
+    assert updated["price"] == payload["price"]
+
+
+def test_delete_item():
+    """Deleting an item should remove it from the store."""
+    response = client.delete("/items/2")
+    assert response.status_code == 204
+
+    # Verify deletion
+    list_response = client.get("/items")
+    ids = {item["id"] for item in list_response.json()}
+    assert 2 not in ids