Fix CI timezone and fresh settings initialization

backend/app/main.py

@@ -129,7 +129,7 @@ def discover():
 def _validate_settings(payload: dict) -> None:
     try:
         ZoneInfo(payload.get("timezone") or "UTC")
-    except ZoneInfoNotFoundError as exc:
+    except (ValueError, ZoneInfoNotFoundError) as exc:
         raise HTTPException(400, "Timezone must be a valid IANA timezone, for example Europe/Berlin or UTC") from exc
     if payload.get("setup_complete"):
         missing = [