Add "Jetzt entpacken" context menu, fix start freeze on large queues

- New "Jetzt entpacken" right-click option: triggers extraction for
  completed packages regardless of paused/stopped state
- Fix 5-10s freeze when pressing Start after Pause: recoverRetryableItems
  was calling fs.stat on every item (474+); now only checks failed/completed
- Full IPC pipeline: extractNow in manager, controller, preload, renderer

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

src/main/main.ts

@@ -318,6 +318,10 @@ function registerIpcHandlers(): void {
     validateString(packageId, "packageId");
     return controller.retryExtraction(packageId);
   });
+  ipcMain.handle(IPC_CHANNELS.EXTRACT_NOW, (_event: IpcMainInvokeEvent, packageId: string) => {
+    validateString(packageId, "packageId");
+    return controller.extractNow(packageId);
+  });
   ipcMain.handle(IPC_CHANNELS.EXPORT_QUEUE, () => controller.exportQueue());
   ipcMain.handle(IPC_CHANNELS.IMPORT_QUEUE, (_event: IpcMainInvokeEvent, json: string) => {
     validateString(json, "json");