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/set-function-length/env.js

@@ -0,0 +1,25 @@
+'use strict';
+
+var gOPD = require('gopd');
+var bind = require('function-bind');
+
+var unbound = gOPD && gOPD(function () {}, 'length');
+// @ts-expect-error ts(2555) TS is overly strict with .call
+var bound = gOPD && gOPD(bind.call(function () {}), 'length');
+
+var functionsHaveConfigurableLengths = !!(unbound && unbound.configurable);
+
+var functionsHaveWritableLengths = !!(unbound && unbound.writable);
+
+var boundFnsHaveConfigurableLengths = !!(bound && bound.configurable);
+
+var boundFnsHaveWritableLengths = !!(bound && bound.writable);
+
+/** @type {import('./env')} */
+module.exports = {
+	__proto__: null,
+	boundFnsHaveConfigurableLengths: boundFnsHaveConfigurableLengths,
+	boundFnsHaveWritableLengths: boundFnsHaveWritableLengths,
+	functionsHaveConfigurableLengths: functionsHaveConfigurableLengths,
+	functionsHaveWritableLengths: functionsHaveWritableLengths
+};