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/regeneratorValues.js

@@ -0,0 +1,19 @@
+import _typeof from "./typeof.js";
+function _regeneratorValues(e) {
+  if (null != e) {
+    var t = e["function" == typeof Symbol && Symbol.iterator || "@@iterator"],
+      r = 0;
+    if (t) return t.call(e);
+    if ("function" == typeof e.next) return e;
+    if (!isNaN(e.length)) return {
+      next: function next() {
+        return e && r >= e.length && (e = void 0), {
+          value: e && e[r++],
+          done: !e
+        };
+      }
+    };
+  }
+  throw new TypeError(_typeof(e) + " is not iterable");
+}
+export { _regeneratorValues as default };