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-streams/isSupported.js

@@ -0,0 +1,24 @@
+/*
+  Copyright 2018 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 { canConstructReadableStream } from 'workbox-core/_private/canConstructReadableStream.js';
+import './_version.js';
+/**
+ * This is a utility method that determines whether the current browser supports
+ * the features required to create streamed responses. Currently, it checks if
+ * [`ReadableStream`](https://developer.mozilla.org/en-US/docs/Web/API/ReadableStream/ReadableStream)
+ * can be created.
+ *
+ * @return {boolean} `true`, if the current browser meets the requirements for
+ * streaming responses, and `false` otherwise.
+ *
+ * @memberof workbox-streams
+ */
+function isSupported() {
+    return canConstructReadableStream();
+}
+export { isSupported };