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-precaching/index.d.ts

@@ -0,0 +1,27 @@
+import { addPlugins } from './addPlugins.js';
+import { addRoute } from './addRoute.js';
+import { cleanupOutdatedCaches } from './cleanupOutdatedCaches.js';
+import { createHandlerBoundToURL } from './createHandlerBoundToURL.js';
+import { getCacheKeyForURL } from './getCacheKeyForURL.js';
+import { matchPrecache } from './matchPrecache.js';
+import { precache } from './precache.js';
+import { precacheAndRoute } from './precacheAndRoute.js';
+import { PrecacheController } from './PrecacheController.js';
+import { PrecacheRoute } from './PrecacheRoute.js';
+import { PrecacheStrategy } from './PrecacheStrategy.js';
+import { PrecacheFallbackPlugin } from './PrecacheFallbackPlugin.js';
+import './_version.js';
+/**
+ * Most consumers of this module will want to use the
+ * {@link workbox-precaching.precacheAndRoute}
+ * method to add assets to the cache and respond to network requests with these
+ * cached assets.
+ *
+ * If you require more control over caching and routing, you can use the
+ * {@link workbox-precaching.PrecacheController}
+ * interface.
+ *
+ * @module workbox-precaching
+ */
+export { addPlugins, addRoute, cleanupOutdatedCaches, createHandlerBoundToURL, getCacheKeyForURL, matchPrecache, precache, precacheAndRoute, PrecacheController, PrecacheRoute, PrecacheStrategy, PrecacheFallbackPlugin, };
+export * from './_types.js';