feat: implement broker credential repository with upsert and list operations

- Add BrokerCredential to domain models and repositories
- Implement upsert_broker_credential() for credential storage and rotation
- Implement list_broker_credentials() for credential retrieval
- Implement delete_broker_credential() for credential removal
- Add broker_credentials table schema with (user_id, broker) composite key
- Implement credential version tracking and last_rotated_at timestamps
- Add FakeRepo support for broker credential CRUD operations
- Add comprehensive test coverage for broker credential lifecycle

app/repositories/postgres.py

@@ -11,7 +11,7 @@ from typing import Any
 import psycopg
 from psycopg import sql
 
-from app.domain.models import AuthToken, Daemon, LedgerEntry, Portfolio, PortfolioComment, PortfolioTag, StrategySet, TokenPrincipal, User
+from app.domain.models import AuthToken, BrokerCredential, Daemon, LedgerEntry, Portfolio, PortfolioComment, PortfolioTag, StrategySet, TokenPrincipal, User
 
 _SELECT_USER = """
     SELECT
@@ -331,6 +331,19 @@ class PostgresPortfolioRepository:
             daemon_id=row[11] if len(row) > 11 else None,
         )
 
+    @staticmethod
+    def _row_to_broker_credential(row: Any) -> BrokerCredential:
+        if row is None:
+            raise ValueError("브로커 인증 정보를 찾을 수 없습니다")
+        return BrokerCredential(
+            user_id=row[0],
+            broker=row[1],
+            account_ref=row[2],
+            encrypted_payload=row[3],
+            credential_version=int(row[4]) if len(row) > 4 else 1,
+            last_rotated_at=row[5] if len(row) > 5 else None,
+        )
+
     @staticmethod
     def _row_to_portfolio(row: Any) -> Portfolio:
         if row is None:
@@ -552,6 +565,60 @@ class PostgresPortfolioRepository:
                 (user_id,),
             )
 
+    def upsert_broker_credential(
+        self,
+        user_id: str,
+        broker: str,
+        *,
+        account_ref: str,
+        encrypted_payload: str,
+    ) -> BrokerCredential:
+        self.ensure_schema()
+        with self._connect().cursor() as cur:
+            cur.execute("SELECT 1 FROM users WHERE id = %s", (user_id,))
+            if cur.fetchone() is None:
+                raise ValueError("사용자를 찾을 수 없습니다")
+            cur.execute(
+                """
+                INSERT INTO broker_credentials (user_id, broker, account_ref, encrypted_payload)
+                VALUES (%s, %s, %s, %s)
+                ON CONFLICT (user_id, broker) DO UPDATE
+                SET account_ref = EXCLUDED.account_ref,
+                    encrypted_payload = EXCLUDED.encrypted_payload,
+                    credential_version = broker_credentials.credential_version + 1,
+                    last_rotated_at = NOW()
+                RETURNING user_id, broker, account_ref, encrypted_payload, credential_version, last_rotated_at
+                """,
+                (user_id, broker, account_ref, encrypted_payload),
+            )
+            row = cur.fetchone()
+        return self._row_to_broker_credential(row)
+
+    def list_broker_credentials(self, user_id: str) -> list[BrokerCredential]:
+        self.ensure_schema()
+        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 delete_broker_credential(self, user_id: str, broker: str) -> bool:
+        self.ensure_schema()
+        with self._connect().cursor() as cur:
+            cur.execute(
+                "DELETE FROM broker_credentials WHERE user_id = %s AND broker = %s RETURNING user_id",
+                (user_id, broker),
+            )
+            row = cur.fetchone()
+        return row is not None
+
     def create_auth_token(
         self,
         user_id: str,