fix(migration): preserve and recover legacy desktop sources (#1550)

* fix(migration): recover legacy desktop sources without replacing current data

* test(migration): cover legacy recovery IPC contracts

* test(migration): use static legacy Electron bootstrap

apps/electron-backend/src/app/workers/database.worker.ts

@@ -1,3 +1,4 @@
+import { migrateAppPlaylists } from '../database/operations/playlist-migration.operations';
 import {
     closeWorkerDatabase,
     getWorkerDatabase,
@@ -679,6 +680,14 @@ async function executeRequest(
             );
         }
 
+        case 'DB_MIGRATE_APP_PLAYLISTS': {
+            const payload = message.payload as {
+                playlists: Record<string, unknown>[];
+                key?: string;
+            };
+            return migrateAppPlaylists(db, payload.playlists, payload.key);
+        }
+
         case 'DB_UPSERT_APP_PLAYLISTS': {
             return upsertAppPlaylists(
                 db,