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/translate-url-to-sourcemap-paths.js

@@ -0,0 +1,33 @@
+"use strict";
+/*
+  Copyright 2021 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.translateURLToSourcemapPaths = void 0;
+const fs_extra_1 = __importDefault(require("fs-extra"));
+const upath_1 = __importDefault(require("upath"));
+const errors_1 = require("./errors");
+function translateURLToSourcemapPaths(url, swSrc, swDest) {
+    let destPath = undefined;
+    let srcPath = undefined;
+    let warning = undefined;
+    if (url && !url.startsWith('data:')) {
+        const possibleSrcPath = upath_1.default.resolve(upath_1.default.dirname(swSrc), url);
+        if (fs_extra_1.default.existsSync(possibleSrcPath)) {
+            srcPath = possibleSrcPath;
+            destPath = upath_1.default.resolve(upath_1.default.dirname(swDest), url);
+        }
+        else {
+            warning = `${errors_1.errors['cant-find-sourcemap']} ${possibleSrcPath}`;
+        }
+    }
+    return { destPath, srcPath, warning };
+}
+exports.translateURLToSourcemapPaths = translateURLToSourcemapPaths;