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-routing/utils/normalizeHandler.js

@@ -0,0 +1,40 @@
+/*
+  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 '../_version.js';
+/**
+ * @param {function()|Object} handler Either a function, or an object with a
+ * 'handle' method.
+ * @return {Object} An object with a handle method.
+ *
+ * @private
+ */
+export const normalizeHandler = (handler) => {
+    if (handler && typeof handler === 'object') {
+        if (process.env.NODE_ENV !== 'production') {
+            assert.hasMethod(handler, 'handle', {
+                moduleName: 'workbox-routing',
+                className: 'Route',
+                funcName: 'constructor',
+                paramName: 'handler',
+            });
+        }
+        return handler;
+    }
+    else {
+        if (process.env.NODE_ENV !== 'production') {
+            assert.isType(handler, 'function', {
+                moduleName: 'workbox-routing',
+                className: 'Route',
+                funcName: 'constructor',
+                paramName: 'handler',
+            });
+        }
+        return { handle: handler };
+    }
+};