fix(downloads): harden queue and lifecycle synchronization

Serialize queue controls, make multi-item moves atomic, await stale enqueue cleanup, and guard late media and progress events. Add deterministic table sorting and regression coverage for worst-case lifecycle races.

src/ipc.ts

@@ -82,6 +82,7 @@ type CommandMap = {
   cancel_enqueue_generation: { args: { id: string; generation: string }; result: void };
   enqueue_many: { args: { items: EnqueueItem[] }; result: import('./bindings/EnqueueResult').EnqueueResult[] };
   move_in_queue: { args: { id: string; queueId: string; direction: 'up' | 'down' }; result: string[] };
+  move_many_in_queue: { args: { ids: string[]; queueId: string; direction: 'up' | 'down' }; result: string[] };
   remove_from_queue: { args: { id: string }; result: boolean };
 };