prepare fastapi root layout for server deployment

app/repositories/audit_repository.py

@@ -0,0 +1,16 @@
+from sqlalchemy.orm import Session
+
+from app.models.audit import AuditLog
+
+
+class AuditRepository:
+    """审计仓储：负责写入关键业务动作的审计日志。"""
+
+    def __init__(self, db: Session) -> None:
+        self.db = db
+
+    def create(self, log: AuditLog) -> AuditLog:
+        """审计写入：保存一条审计日志并刷新主键。"""
+        self.db.add(log)
+        self.db.flush()
+        return log