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/iterableToArrayLimit.js

@@ -0,0 +1,28 @@
+function _iterableToArrayLimit(r, l) {
+  var t = null == r ? null : "undefined" != typeof Symbol && r[Symbol.iterator] || r["@@iterator"];
+  if (null != t) {
+    var e,
+      n,
+      i,
+      u,
+      a = [],
+      f = !0,
+      o = !1;
+    try {
+      if (i = (t = t.call(r)).next, 0 === l) {
+        if (Object(t) !== t) return;
+        f = !1;
+      } else for (; !(f = (e = i.call(t)).done) && (a.push(e.value), a.length !== l); f = !0);
+    } catch (r) {
+      o = !0, n = r;
+    } finally {
+      try {
+        if (!f && null != t["return"] && (u = t["return"](), Object(u) !== u)) return;
+      } finally {
+        if (o) throw n;
+      }
+    }
+    return a;
+  }
+}
+module.exports = _iterableToArrayLimit, module.exports.__esModule = true, module.exports["default"] = module.exports;