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/strategy.d.ts

@@ -0,0 +1,24 @@
+import { RouteHandlerCallback, RouteHandlerCallbackOptions } from 'workbox-core/types.js';
+import { StreamSource } from './_types.js';
+import './_version.js';
+export interface StreamsHandlerCallback {
+    ({ url, request, event, params }: RouteHandlerCallbackOptions): Promise<StreamSource> | StreamSource;
+}
+/**
+ * A shortcut to create a strategy that could be dropped-in to Workbox's router.
+ *
+ * On browsers that do not support constructing new `ReadableStream`s, this
+ * strategy will automatically wait for all the `sourceFunctions` to complete,
+ * and create a final response that concatenates their values together.
+ *
+ * @param {Array<function({event, request, url, params})>} sourceFunctions
+ * An array of functions similar to {@link workbox-routing~handlerCallback}
+ * but that instead return a {@link workbox-streams.StreamSource} (or a
+ * Promise which resolves to one).
+ * @param {HeadersInit} [headersInit] If there's no `Content-Type` specified,
+ * `'text/html'` will be used by default.
+ * @return {workbox-routing~handlerCallback}
+ * @memberof workbox-streams
+ */
+declare function strategy(sourceFunctions: StreamsHandlerCallback[], headersInit: HeadersInit): RouteHandlerCallback;
+export { strategy };