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/helper-create-regexp-features-plugin/lib/features.js

@@ -0,0 +1,30 @@
+"use strict";
+
+Object.defineProperty(exports, "__esModule", {
+  value: true
+});
+exports.FEATURES = void 0;
+exports.enableFeature = enableFeature;
+exports.featuresKey = void 0;
+exports.hasFeature = hasFeature;
+exports.runtimeKey = void 0;
+const FEATURES = exports.FEATURES = Object.freeze({
+  unicodeFlag: 1 << 0,
+  dotAllFlag: 1 << 1,
+  unicodePropertyEscape: 1 << 2,
+  namedCaptureGroups: 1 << 3,
+  unicodeSetsFlag_syntax: 1 << 4,
+  unicodeSetsFlag: 1 << 5,
+  duplicateNamedCaptureGroups: 1 << 6,
+  modifiers: 1 << 7
+});
+const featuresKey = exports.featuresKey = "@babel/plugin-regexp-features/featuresKey";
+const runtimeKey = exports.runtimeKey = "@babel/plugin-regexp-features/runtimeKey";
+function enableFeature(features, feature) {
+  return features | feature;
+}
+function hasFeature(features, feature) {
+  return !!(features & feature);
+}
+
+//# sourceMappingURL=features.js.map