fix(backend): redact retryable MAX storage failures

Refs #82

app/api/max_notifications.py

@@ -10,6 +10,7 @@ from fastapi import APIRouter, Depends, HTTPException, Request
 from fastapi.security import HTTPAuthorizationCredentials, HTTPBearer
 from pydantic import BaseModel, ConfigDict
 from sqlalchemy import select
+from sqlalchemy.exc import SQLAlchemyError
 
 from app.config import get_settings
 from app.core import clock
@@ -106,5 +107,9 @@ async def webhook(request: Request) -> dict[str, bool]:
         raise HTTPException(422, "event must be an object")
     from app.channels.max_bot import handle_update
 
-    await handle_update(event)
+    try:
+        await handle_update(event)
+    except SQLAlchemyError:
+        # Let MAX retry; do not log DB exception parameters containing identity data.
+        raise HTTPException(503, "notification storage unavailable") from None
     return {"success": True}