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/workbox-build/build/generate-sw.d.ts

@@ -0,0 +1,47 @@
+import { BuildResult, GenerateSWOptions } from './types';
+/**
+ * This method creates a list of URLs to precache, referred to as a "precache
+ * manifest", based on the options you provide.
+ *
+ * It also takes in additional options that configures the service worker's
+ * behavior, like any `runtimeCaching` rules it should use.
+ *
+ * Based on the precache manifest and the additional configuration, it writes
+ * a ready-to-use service worker file to disk at `swDest`.
+ *
+ * ```
+ * // The following lists some common options; see the rest of the documentation
+ * // for the full set of options and defaults.
+ * const {count, size, warnings} = await generateSW({
+ *   dontCacheBustURLsMatching: [new RegExp('...')],
+ *   globDirectory: '...',
+ *   globPatterns: ['...', '...'],
+ *   maximumFileSizeToCacheInBytes: ...,
+ *   navigateFallback: '...',
+ *   runtimeCaching: [{
+ *     // Routing via a matchCallback function:
+ *     urlPattern: ({request, url}) => ...,
+ *     handler: '...',
+ *     options: {
+ *       cacheName: '...',
+ *       expiration: {
+ *         maxEntries: ...,
+ *       },
+ *     },
+ *   }, {
+ *     // Routing via a RegExp:
+ *     urlPattern: new RegExp('...'),
+ *     handler: '...',
+ *     options: {
+ *       cacheName: '...',
+ *       plugins: [..., ...],
+ *     },
+ *   }],
+ *   skipWaiting: ...,
+ *   swDest: '...',
+ * });
+ * ```
+ *
+ * @memberof workbox-build
+ */
+export declare function generateSW(config: GenerateSWOptions): Promise<BuildResult>;