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/es-abstract/5/Canonicalize.js

@@ -0,0 +1,38 @@
+'use strict';
+
+var $TypeError = require('es-errors/type');
+
+var callBound = require('call-bound');
+
+var $charCodeAt = callBound('String.prototype.charCodeAt');
+var $toUpperCase = callBound('String.prototype.toUpperCase');
+
+// https://262.ecma-international.org/5.1/#sec-15.10.2.8
+
+module.exports = function Canonicalize(ch, IgnoreCase) {
+	if (typeof ch !== 'string' || ch.length !== 1) {
+		throw new $TypeError('Assertion failed: `ch` must be a character');
+	}
+
+	if (typeof IgnoreCase !== 'boolean') {
+		throw new $TypeError('Assertion failed: `IgnoreCase` must be a Boolean');
+	}
+
+	if (!IgnoreCase) {
+		return ch; // step 1
+	}
+
+	var u = $toUpperCase(ch); // step 2
+
+	if (u.length !== 1) {
+		return ch; // step 3
+	}
+
+	var cu = u; // step 4
+
+	if ($charCodeAt(ch, 0) >= 128 && $charCodeAt(cu, 0) < 128) {
+		return ch; // step 5
+	}
+
+	return cu;
+};