test+docs(updates): cover pending-after-register over HTTP and update rest.rst

Extend test_updates.test.py with an integration test that registers a
package and immediately fetches /updates/{id}/status, asserting a 200
response with status=pending and no progress/error keys - the end-to-end
counterpart to the new UpdateManagerTest.StatusPendingRightAfterRegister
unit test.

Update docs/api/rest.rst to describe the new contract: after a
successful POST /api/v1/updates, GET /api/v1/updates/{id}/status
immediately returns 200 with {"status":"pending"}. 404 is reserved for
packages that are not registered.

Author: bburda

docs/api/rest.rst

@@ -1143,6 +1143,10 @@ Without such a plugin, all endpoints return ``501 Not Implemented``.
 
    **Status values:** ``pending``, ``inProgress``, ``completed``, ``failed``
 
+   A successful ``POST /api/v1/updates`` seeds a ``pending`` status for the package,
+   so this endpoint returns ``200`` with ``{"status": "pending"}`` immediately after
+   registration, before any ``prepare`` or ``execute`` call.
+
    When ``status`` is ``failed``, an ``error`` object is included:
 
    .. code-block:: json
@@ -1155,7 +1159,7 @@ Without such a plugin, all endpoints return ``501 Not Implemented``.
         }
       }
 
-   - **404 Not Found:** No status available (package not found or no operation started)
+   - **404 Not Found:** Package is not registered
 
 Cyclic Subscriptions
 --------------------

src/ros2_medkit_integration_tests/test/features/test_updates.test.py

@@ -353,6 +353,20 @@ class TestUpdatesPrepareExecute(_UpdatesTestMixin, GatewayTestCase):
     BASE_URL = f'http://127.0.0.1:{PORT_WITH_PLUGIN}{API_BASE_PATH}'
     MIN_EXPECTED_APPS = 0
 
+    # @verifies REQ_INTEROP_094
+    def test_00_status_pending_right_after_register(self):
+        """GET /status returns 200 pending immediately after POST /updates."""
+        self.register_package('test-pending-after-register')
+        r = requests.get(
+            f'{self.BASE_URL}/updates/test-pending-after-register/status',
+            timeout=5,
+        )
+        self.assertEqual(r.status_code, 200)
+        data = r.json()
+        self.assertEqual(data.get('status'), 'pending')
+        self.assertNotIn('progress', data)
+        self.assertNotIn('error', data)
+
     # @verifies REQ_INTEROP_091
     def test_01_prepare_returns_202(self):
         """PUT /updates/{id}/prepare returns 202 Accepted."""