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-core/cacheNames.js

@@ -0,0 +1,42 @@
+/*
+  Copyright 2019 Google LLC
+
+  Use of this source code is governed by an MIT-style
+  license that can be found in the LICENSE file or at
+  https://opensource.org/licenses/MIT.
+*/
+import { cacheNames as _cacheNames } from './_private/cacheNames.js';
+import './_version.js';
+/**
+ * Get the current cache names and prefix/suffix used by Workbox.
+ *
+ * `cacheNames.precache` is used for precached assets,
+ * `cacheNames.googleAnalytics` is used by `workbox-google-analytics` to
+ * store `analytics.js`, and `cacheNames.runtime` is used for everything else.
+ *
+ * `cacheNames.prefix` can be used to retrieve just the current prefix value.
+ * `cacheNames.suffix` can be used to retrieve just the current suffix value.
+ *
+ * @return {Object} An object with `precache`, `runtime`, `prefix`, and
+ *     `googleAnalytics` properties.
+ *
+ * @memberof workbox-core
+ */
+const cacheNames = {
+    get googleAnalytics() {
+        return _cacheNames.getGoogleAnalyticsName();
+    },
+    get precache() {
+        return _cacheNames.getPrecacheName();
+    },
+    get prefix() {
+        return _cacheNames.getPrefix();
+    },
+    get runtime() {
+        return _cacheNames.getRuntimeName();
+    },
+    get suffix() {
+        return _cacheNames.getSuffix();
+    },
+};
+export { cacheNames };