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/skipWaiting.js

@@ -0,0 +1,27 @@
+/*
+  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 { logger } from './_private/logger.js';
+import './_version.js';
+/**
+ * This method is deprecated, and will be removed in Workbox v7.
+ *
+ * Calling self.skipWaiting() is equivalent, and should be used instead.
+ *
+ * @memberof workbox-core
+ */
+function skipWaiting() {
+    // Just call self.skipWaiting() directly.
+    // See https://github.com/GoogleChrome/workbox/issues/2525
+    if (process.env.NODE_ENV !== 'production') {
+        logger.warn(`skipWaiting() from workbox-core is no longer recommended ` +
+            `and will be removed in Workbox v7. Using self.skipWaiting() instead ` +
+            `is equivalent.`);
+    }
+    void self.skipWaiting();
+}
+export { skipWaiting };