feat: notification center backend core (PR-1)

- Add notifications table with Alembic migration
- Notification model with user-scoped indexing and partial index on unread
- NotificationService singleton with create/list/count/mark-read/dismiss
- FastAPI router: GET /notifications, GET /unread, PATCH /{id}/read,
  POST /mark-all-read, DELETE /{id}
- Mute categories filtering from UserConfig
- 13 unit tests for NotificationService
- 10 integration tests for API endpoints
- Updated test_models.py with new table registration

Quality gates: pytest 23 new passed, ruff clean

apps/api/tests/integration/test_models.py

@@ -16,7 +16,6 @@ def test_base_metadata_collects_declared_tables() -> None:
 
 
 @pytest.mark.integration
-
 def test_shared_mixins_define_expected_columns() -> None:
     assert "id" in UUIDPrimaryKeyMixin.__dict__
     assert "created_at" in TimestampMixin.__dict__
@@ -24,20 +23,26 @@ def test_shared_mixins_define_expected_columns() -> None:
 
 
 @pytest.mark.integration
-
 def test_expected_tables_are_registered() -> None:
     assert set(Base.metadata.tables) == {
-        "refresh_tokens",
+        "config_profile_includes",
+        "config_profiles",
         "git_repositories",
+        "health_checks",
+        "instance_events",
+        "notifications",
         "projects",
         "ssh_keys",
+        "terminal_sessions",
+        "tool_definition_manifests",
+        "tool_instances",
+        "tool_types",
         "user_configs",
         "users",
     }
 
 
 @pytest.mark.integration
-
 def test_user_table_has_required_columns() -> None:
     columns = User.__table__.columns
 
@@ -56,7 +61,6 @@ def test_user_table_has_required_columns() -> None:
 
 
 @pytest.mark.integration
-
 def test_project_relationships_point_to_owner_and_default_ssh_key() -> None:
     owner_fk = next(iter(Project.__table__.c.owner_id.foreign_keys))
     ssh_fk = next(iter(Project.__table__.c.default_ssh_key_id.foreign_keys))
@@ -68,7 +72,6 @@ def test_project_relationships_point_to_owner_and_default_ssh_key() -> None:
 
 
 @pytest.mark.integration
-
 def test_repository_and_user_config_relationships_are_registered() -> None:
     project_fk = next(iter(GitRepository.__table__.c.project_id.foreign_keys))
     owner_fk = next(iter(GitRepository.__table__.c.owner_id.foreign_keys))
@@ -84,9 +87,13 @@ def test_repository_and_user_config_relationships_are_registered() -> None:
 
 @pytest.mark.asyncio
 @pytest.mark.integration
-
 async def test_async_session_can_insert_and_load_user(db_session: AsyncSession) -> None:
-    user = User(email="dev@headquarter.local", name="Dev User", authentik_id="dev-user", avatar_url=None)
+    user = User(
+        email="dev@headquarter.local",
+        name="Dev User",
+        authentik_id="dev-user",
+        avatar_url=None,
+    )
 
     db_session.add(user)
     await db_session.commit()