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/preset-env/lib/targets-parser.js

@@ -0,0 +1,20 @@
+"use strict";
+
+Object.defineProperty(exports, "__esModule", {
+  value: true
+});
+Object.defineProperty(exports, "default", {
+  enumerable: true,
+  get: function () {
+    return _helperCompilationTargets.default;
+  }
+});
+Object.defineProperty(exports, "isBrowsersQueryValid", {
+  enumerable: true,
+  get: function () {
+    return _helperCompilationTargets.isBrowsersQueryValid;
+  }
+});
+var _helperCompilationTargets = require("@babel/helper-compilation-targets");
+
+//# sourceMappingURL=targets-parser.js.map