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/app-controller.ts

@@ -212,6 +212,10 @@ export class AppController {
     this.manager.retryExtraction(packageId);
   }
 
+  public extractNow(packageId: string): void {
+    this.manager.extractNow(packageId);
+  }
+
   public cancelPackage(packageId: string): void {
     this.manager.cancelPackage(packageId);
   }