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/get-symbol-description/getInferredName.js

@@ -0,0 +1,13 @@
+'use strict';
+
+/** @type {NonNullable<import('./getInferredName')> | undefined} */
+var getInferredName;
+try {
+	// eslint-disable-next-line no-new-func, no-extra-parens
+	getInferredName = /** @type {NonNullable<import('./getInferredName')>} */ (Function('s', 'return { [s]() {} }[s].name;'));
+} catch (e) {}
+
+var inferred = function () {};
+
+/** @type {import('./getInferredName')} */
+module.exports = getInferredName && inferred.name === 'inferred' ? getInferredName : null;