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/consoleFunc.js

@@ -0,0 +1,31 @@
+'use strict';
+
+Object.defineProperty(exports, "__esModule", {
+    value: true
+});
+exports.default = consoleFunc;
+
+var _wrapAsync = require('./wrapAsync.js');
+
+var _wrapAsync2 = _interopRequireDefault(_wrapAsync);
+
+function _interopRequireDefault(obj) { return obj && obj.__esModule ? obj : { default: obj }; }
+
+function consoleFunc(name) {
+    return (fn, ...args) => (0, _wrapAsync2.default)(fn)(...args, (err, ...resultArgs) => {
+        /* istanbul ignore else */
+        if (typeof console === 'object') {
+            /* istanbul ignore else */
+            if (err) {
+                /* istanbul ignore else */
+                if (console.error) {
+                    console.error(err);
+                }
+            } else if (console[name]) {
+                /* istanbul ignore else */
+                resultArgs.forEach(x => console[name](x));
+            }
+        }
+    });
+}
+module.exports = exports.default;