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/preload/preload.ts

@@ -48,6 +48,7 @@ const api: ElectronApi = {
   importBackup: (): Promise<{ restored: boolean; message: string }> => ipcRenderer.invoke(IPC_CHANNELS.IMPORT_BACKUP),
   openLog: (): Promise<void> => ipcRenderer.invoke(IPC_CHANNELS.OPEN_LOG),
   retryExtraction: (packageId: string): Promise<void> => ipcRenderer.invoke(IPC_CHANNELS.RETRY_EXTRACTION, packageId),
+  extractNow: (packageId: string): Promise<void> => ipcRenderer.invoke(IPC_CHANNELS.EXTRACT_NOW, packageId),
   onStateUpdate: (callback: (snapshot: UiSnapshot) => void): (() => void) => {
     const listener = (_event: unknown, snapshot: UiSnapshot): void => callback(snapshot);
     ipcRenderer.on(IPC_CHANNELS.STATE_UPDATE, listener);