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/inherits.js

@@ -0,0 +1,14 @@
+var setPrototypeOf = require("./setPrototypeOf.js");
+function _inherits(t, e) {
+  if ("function" != typeof e && null !== e) throw new TypeError("Super expression must either be null or a function");
+  t.prototype = Object.create(e && e.prototype, {
+    constructor: {
+      value: t,
+      writable: !0,
+      configurable: !0
+    }
+  }), Object.defineProperty(t, "prototype", {
+    writable: !1
+  }), e && setPrototypeOf(t, e);
+}
+module.exports = _inherits, module.exports.__esModule = true, module.exports["default"] = module.exports;