Mobile App: Registration schema improvements (#21850)

* Update registration schema to add os_name (required) and make app_name required

* Ensure that a provided app_component is valid and available

* Ensure that component DEPENDENCIES declares mobile_app

* Update homeassistant/helpers/config_validation.py

* Standardize error responses

* Dont generalize REGISTER_BAD_COMPONENT

* Fix tests after merge

tests/components/mobile_app/test_http_api.py

@@ -63,3 +63,28 @@ async def test_registration(hass_client, authed_api_client):  # noqa: F811
     decrypted_data = decrypted_data.decode("utf-8")
 
     assert json.loads(decrypted_data) == {'rendered': 'Hello world'}
+
+
+async def test_register_invalid_component(authed_api_client):  # noqa: F811
+    """Test that registration with invalid component fails."""
+    resp = await authed_api_client.post(
+        '/api/mobile_app/registrations', json={
+            'app_component': 'will_never_be_valid',
+            'app_data': {'foo': 'bar'},
+            'app_id': 'io.homeassistant.mobile_app_test',
+            'app_name': 'Mobile App Tests',
+            'app_version': '1.0.0',
+            'device_name': 'Test 1',
+            'manufacturer': 'mobile_app',
+            'model': 'Test',
+            'os_name': 'Linux',
+            'os_version': '1.0',
+            'supports_encryption': True
+        }
+    )
+
+    assert resp.status == 400
+    register_json = await resp.json()
+    assert 'error' in register_json
+    assert register_json['success'] is False
+    assert register_json['error']['code'] == 'invalid_component'