feat(REQ-005): implement TrEx Basic V1 API contract with auth, assets, ledger, and user endpoints

- Add V1 API routes for assets, ledger, and user info with complete CRUD operations
- Implement authentication scopes and request validation via auth_routes.py
- Extend schemas with V1-specific models for accounts, holdings, and positions
- Add database queries and aggregations for P&L, performance, and account data
- Include comprehensive test coverage for all V1 endpoints and integration flows
- Update batch and release documentation with implementation and verification evidence
- Sync project structure and runtime flows per V1 API contract requirements

Closes implementation phase of BAT-001 (TrEx Basic V1 API Contract)

app/repositories/postgres.py

@@ -1334,6 +1334,20 @@ class PostgresPortfolioRepository:
             return None
         return self._row_to_broker_credential(row)
 
+    def list_broker_credentials(self, user_id: str) -> list[BrokerCredential]:
+        with self._connect().cursor() as cur:
+            cur.execute(
+                """
+                SELECT user_id, broker, account_ref, encrypted_payload, credential_version, last_rotated_at
+                FROM broker_credentials
+                WHERE user_id = %s
+                ORDER BY broker ASC
+                """,
+                (user_id,),
+            )
+            rows = cur.fetchall()
+        return [self._row_to_broker_credential(row) for row in rows]
+
     def upsert_broker_credential(
         self,
         user_id: str,