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/@babel/runtime/helpers/objectSpread.js

@@ -0,0 +1,14 @@
+var defineProperty = require("./defineProperty.js");
+function _objectSpread(e) {
+  for (var r = 1; r < arguments.length; r++) {
+    var t = null != arguments[r] ? Object(arguments[r]) : {},
+      o = Object.keys(t);
+    "function" == typeof Object.getOwnPropertySymbols && o.push.apply(o, Object.getOwnPropertySymbols(t).filter(function (e) {
+      return Object.getOwnPropertyDescriptor(t, e).enumerable;
+    })), o.forEach(function (r) {
+      defineProperty(e, r, t[r]);
+    });
+  }
+  return e;
+}
+module.exports = _objectSpread, module.exports.__esModule = true, module.exports["default"] = module.exports;