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/esm/importDeferProxy.js

@@ -0,0 +1,27 @@
+function _importDeferProxy(e) {
+  var t = null,
+    constValue = function constValue(e) {
+      return function () {
+        return e;
+      };
+    },
+    proxy = function proxy(r) {
+      return function (n, o, f) {
+        return null === t && (t = e()), r(t, o, f);
+      };
+    };
+  return new Proxy({}, {
+    defineProperty: constValue(!1),
+    deleteProperty: constValue(!1),
+    get: proxy(Reflect.get),
+    getOwnPropertyDescriptor: proxy(Reflect.getOwnPropertyDescriptor),
+    getPrototypeOf: constValue(null),
+    isExtensible: constValue(!1),
+    has: proxy(Reflect.has),
+    ownKeys: proxy(Reflect.ownKeys),
+    preventExtensions: constValue(!0),
+    set: constValue(!1),
+    setPrototypeOf: constValue(!1)
+  });
+}
+export { _importDeferProxy as default };