Refactor app initialization logic

ts/types/Storage.d.ts

@@ -211,6 +211,8 @@ export type StorageAccessType = {
   // The `firstAppVersion` present on an BackupInfo from an imported backup.
   restoredBackupFirstAppVersion: string;
 
+  postRegistrationSyncsStatus: 'incomplete' | 'complete';
+
   // Deprecated
   'challenge:retry-message-ids': never;
   nextSignedKeyRotationTime: number;