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-precaching/utils/printInstallDetails.js

@@ -0,0 +1,48 @@
+/*
+  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 { logger } from 'workbox-core/_private/logger.js';
+import '../_version.js';
+/**
+ * @param {string} groupTitle
+ * @param {Array<string>} urls
+ *
+ * @private
+ */
+function _nestedGroup(groupTitle, urls) {
+    if (urls.length === 0) {
+        return;
+    }
+    logger.groupCollapsed(groupTitle);
+    for (const url of urls) {
+        logger.log(url);
+    }
+    logger.groupEnd();
+}
+/**
+ * @param {Array<string>} urlsToPrecache
+ * @param {Array<string>} urlsAlreadyPrecached
+ *
+ * @private
+ * @memberof workbox-precaching
+ */
+export function printInstallDetails(urlsToPrecache, urlsAlreadyPrecached) {
+    const precachedCount = urlsToPrecache.length;
+    const alreadyPrecachedCount = urlsAlreadyPrecached.length;
+    if (precachedCount || alreadyPrecachedCount) {
+        let message = `Precaching ${precachedCount} file${precachedCount === 1 ? '' : 's'}.`;
+        if (alreadyPrecachedCount > 0) {
+            message +=
+                ` ${alreadyPrecachedCount} ` +
+                    `file${alreadyPrecachedCount === 1 ? ' is' : 's are'} already cached.`;
+        }
+        logger.groupCollapsed(message);
+        _nestedGroup(`View newly precached URLs.`, urlsToPrecache);
+        _nestedGroup(`View previously precached URLs.`, urlsAlreadyPrecached);
+        logger.groupEnd();
+    }
+}