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-recipes/staticResourceCache.d.ts

@@ -0,0 +1,21 @@
+import { RouteMatchCallback, WorkboxPlugin } from 'workbox-core/types.js';
+import './_version.js';
+export interface StaticResourceOptions {
+    cacheName?: string;
+    matchCallback?: RouteMatchCallback;
+    plugins?: Array<WorkboxPlugin>;
+    warmCache?: Array<string>;
+}
+/**
+ * An implementation of the [CSS and JavaScript files recipe]{@link https://developers.google.com/web/tools/workbox/guides/common-recipes#cache_css_and_javascript_files}
+ *
+ * @memberof workbox-recipes
+ *
+ * @param {Object} [options]
+ * @param {string} [options.cacheName] Name for cache. Defaults to static-resources
+ * @param {RouteMatchCallback} [options.matchCallback] Workbox callback function to call to match to. Defaults to request.destination === 'style' || request.destination === 'script' || request.destination === 'worker';
+ * @param {WorkboxPlugin[]} [options.plugins] Additional plugins to use for this recipe
+ * @param {string[]} [options.warmCache] Paths to call to use to warm this cache
+ */
+declare function staticResourceCache(options?: StaticResourceOptions): void;
+export { staticResourceCache };