Keep stacked notification images and warn when OEM AUTO_START blocks UnifiedPush.

Attach image thumbnails via MessagingStyle message data so they survive multi-message history, drop useless image filenames, and surface TCL App Boot blocks in settings.

overlay/src/app/utils/backgroundSync.ts

@@ -9,6 +9,8 @@ type UnifiedPushStatus = {
   distributor: string;
   distributors: string[] | string;
   lastFailure?: string;
+  /** OEM App Boot / AUTO_START is blocking distributor broadcasts (e.g. TCL). */
+  autoStartBlocked?: boolean;
 };
 
 type ClearRoomNotificationsResult = {