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-build/build/lib/rebase-path.js

@@ -0,0 +1,24 @@
+"use strict";
+/*
+  Copyright 2019 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.
+*/
+var __importDefault = (this && this.__importDefault) || function (mod) {
+    return (mod && mod.__esModule) ? mod : { "default": mod };
+};
+Object.defineProperty(exports, "__esModule", { value: true });
+exports.rebasePath = void 0;
+const upath_1 = __importDefault(require("upath"));
+function rebasePath({ baseDirectory, file, }) {
+    // The initial path is relative to the current directory, so make it absolute.
+    const absolutePath = upath_1.default.resolve(file);
+    // Convert the absolute path so that it's relative to the baseDirectory.
+    const relativePath = upath_1.default.relative(baseDirectory, absolutePath);
+    // Remove any leading ./ as it won't work in a glob pattern.
+    const normalizedPath = upath_1.default.normalize(relativePath);
+    return normalizedPath;
+}
+exports.rebasePath = rebasePath;