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/async/internal/applyEach.js

@@ -0,0 +1,29 @@
+'use strict';
+
+Object.defineProperty(exports, "__esModule", {
+    value: true
+});
+
+exports.default = function (eachfn) {
+    return function applyEach(fns, ...callArgs) {
+        const go = (0, _awaitify2.default)(function (callback) {
+            var that = this;
+            return eachfn(fns, (fn, cb) => {
+                (0, _wrapAsync2.default)(fn).apply(that, callArgs.concat(cb));
+            }, callback);
+        });
+        return go;
+    };
+};
+
+var _wrapAsync = require('./wrapAsync.js');
+
+var _wrapAsync2 = _interopRequireDefault(_wrapAsync);
+
+var _awaitify = require('./awaitify.js');
+
+var _awaitify2 = _interopRequireDefault(_awaitify);
+
+function _interopRequireDefault(obj) { return obj && obj.__esModule ? obj : { default: obj }; }
+
+module.exports = exports.default;