Add SpoolBuddy quick menu with power control and system commands (#893)

Swipe down from the top of the SpoolBuddy display to open a quick-access
  menu for toggling printer smart plugs and managing the device (restart
  daemon, restart browser, reboot, shutdown). All destructive actions
  require confirmation.

  Backend: new POST /spoolbuddy/devices/{id}/system/command endpoint
  queuing reboot/shutdown/restart_daemon/restart_browser commands.
  Daemon: handles commands via subprocess (sudo reboot, systemctl restart).
  Frontend: SpoolBuddyQuickMenu component, swipe-down gesture detection,
  i18n keys for all 7 locales.

frontend/src/api/client.ts

@@ -5267,6 +5267,12 @@ export const spoolbuddyApi = {
       body: '{}',
     }),
 
+  systemCommand: (deviceId: string, command: 'reboot' | 'shutdown' | 'restart_daemon' | 'restart_browser') =>
+    request<{ status: string; command: string }>(`/spoolbuddy/devices/${deviceId}/system/command`, {
+      method: 'POST',
+      body: JSON.stringify({ command }),
+    }),
+
   queueDiagnostics: (deviceId: string, type: 'nfc' | 'scale' | 'read_tag') =>
     request<{ status: string; diagnostic: string; message: string }>(
       `/spoolbuddy/diagnostics/${deviceId}/run?diagnostic=${type}`,