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/createClass.js

@@ -0,0 +1,13 @@
+var toPropertyKey = require("./toPropertyKey.js");
+function _defineProperties(e, r) {
+  for (var t = 0; t < r.length; t++) {
+    var o = r[t];
+    o.enumerable = o.enumerable || !1, o.configurable = !0, "value" in o && (o.writable = !0), Object.defineProperty(e, toPropertyKey(o.key), o);
+  }
+}
+function _createClass(e, r, t) {
+  return r && _defineProperties(e.prototype, r), t && _defineProperties(e, t), Object.defineProperty(e, "prototype", {
+    writable: !1
+  }), e;
+}
+module.exports = _createClass, module.exports.__esModule = true, module.exports["default"] = module.exports;