refactor: simplify data model by removing unused fields and constraints

- Remove runtime_id from AuthToken model
- Remove market field from Portfolio model
- Remove BrokerCredential and LedgerTrade unused models
- Remove unique constraint on (owner_user_id, name)
- Simplify postgres repository schema and queries
- Clean up auth_service implementation
- Update test suite for simplified model

app/repositories/portfolio_repository.py

@@ -65,14 +65,6 @@ class PortfolioRepository(Protocol):
 
     def revoke_auth_token(self, user_id: str, token_id: str) -> None: ...
 
-    def rotate_service_token(
-        self,
-        token_id: str,
-        token_hash: str,
-        token_prefix: str,
-        runtime_id: str,
-    ) -> AuthToken: ...
-
     def get_service_token_by_name(self, name: str) -> AuthToken | None: ...
 
     def get_token_principal(self, token_hash: str) -> TokenPrincipal | None: ...