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-strategies/src/CacheOnly.ts

@@ -0,0 +1,72 @@
+/*
+  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 {assert} from 'workbox-core/_private/assert.js';
+import {logger} from 'workbox-core/_private/logger.js';
+import {WorkboxError} from 'workbox-core/_private/WorkboxError.js';
+
+import {Strategy} from './Strategy.js';
+import {StrategyHandler} from './StrategyHandler.js';
+import {messages} from './utils/messages.js';
+import './_version.js';
+
+/**
+ * An implementation of a [cache-only](https://developer.chrome.com/docs/workbox/caching-strategies-overview/#cache-only)
+ * request strategy.
+ *
+ * This class is useful if you want to take advantage of any
+ * [Workbox plugins](https://developer.chrome.com/docs/workbox/using-plugins/).
+ *
+ * If there is no cache match, this will throw a `WorkboxError` exception.
+ *
+ * @extends workbox-strategies.Strategy
+ * @memberof workbox-strategies
+ */
+class CacheOnly extends Strategy {
+  /**
+   * @private
+   * @param {Request|string} request A request to run this strategy for.
+   * @param {workbox-strategies.StrategyHandler} handler The event that
+   *     triggered the request.
+   * @return {Promise<Response>}
+   */
+  async _handle(request: Request, handler: StrategyHandler): Promise<Response> {
+    if (process.env.NODE_ENV !== 'production') {
+      assert!.isInstance(request, Request, {
+        moduleName: 'workbox-strategies',
+        className: this.constructor.name,
+        funcName: 'makeRequest',
+        paramName: 'request',
+      });
+    }
+
+    const response = await handler.cacheMatch(request);
+
+    if (process.env.NODE_ENV !== 'production') {
+      logger.groupCollapsed(
+        messages.strategyStart(this.constructor.name, request),
+      );
+      if (response) {
+        logger.log(
+          `Found a cached response in the '${this.cacheName}' ` + `cache.`,
+        );
+        messages.printFinalResponse(response);
+      } else {
+        logger.log(`No response found in the '${this.cacheName}' cache.`);
+      }
+      logger.groupEnd();
+    }
+
+    if (!response) {
+      throw new WorkboxError('no-response', {url: request.url});
+    }
+    return response;
+  }
+}
+
+export {CacheOnly};