fix(rls): 收斂 API DB access context

apps/api/src/services/trust_drift_detector.py

@@ -39,7 +39,7 @@ from dataclasses import dataclass
 import structlog
 from sqlalchemy import func, select
 
-from src.db.base import get_session_factory
+from src.db.base import get_db_context
 from src.db.models import AiGovernanceEvent, PlaybookRecord
 from src.utils.timezone import now_taipei
 
@@ -115,7 +115,7 @@ class TrustDriftDetector:
             TrustDistribution（樣本不足時 drift_detected=False）
         """
         try:
-            async with get_session_factory()() as session:
+            async with get_db_context() as session:
                 # 只計算 approved 狀態的 Playbook
                 total_q = await session.execute(
                     select(func.count()).where(
@@ -215,7 +215,7 @@ class TrustDriftDetector:
     async def save_drift_event(self, dist: TrustDistribution) -> None:
         """將信任度漂移事件寫入 ai_governance_events。"""
         try:
-            async with get_session_factory()() as session:
+            async with get_db_context() as session:
                 event = AiGovernanceEvent(
                     event_type="trust_drift",
                     details={