Add sync error logging, extend error flash, fix unload saves

- Log workforce sync errors to backend stdout so they appear in docker logs
- Extend error flash from 5s to 15s so errors are readable
- Replace sendBeacon (POST-only) with keepalive fetch (PUT) on unload —
  sendBeacon was hitting 404s on all three unload saves

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

frontend/node_modules/vite-plugin-pwa/vue.d.ts

@@ -0,0 +1,19 @@
+declare module 'virtual:pwa-register/vue' {
+  import type { RegisterSWOptions } from 'vite-plugin-pwa/types'
+  // eslint-disable-next-line ts/ban-ts-comment
+  // @ts-ignore ignore when vue is not installed
+  import type { Ref } from 'vue'
+
+  export type { RegisterSWOptions }
+
+  export function useRegisterSW(options?: RegisterSWOptions): {
+    needRefresh: Ref<boolean>
+    offlineReady: Ref<boolean>
+    /**
+     * Reloads the current window to allow the service worker take the control.
+     *
+     * @param reloadPage From version 0.13.2+ this param is not used anymore.
+     */
+    updateServiceWorker: (reloadPage?: boolean) => Promise<void>
+  }
+}