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/shared/ipc.ts

@@ -32,5 +32,6 @@ export const IPC_CHANNELS = {
   EXPORT_BACKUP: "app:export-backup",
   IMPORT_BACKUP: "app:import-backup",
   OPEN_LOG: "app:open-log",
-  RETRY_EXTRACTION: "queue:retry-extraction"
+  RETRY_EXTRACTION: "queue:retry-extraction",
+  EXTRACT_NOW: "queue:extract-now"
 } as const;