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/2023/Canonicalize.js

@@ -0,0 +1,52 @@
+'use strict';
+
+var $TypeError = require('es-errors/type');
+
+var callBound = require('call-bound');
+var hasOwn = require('hasown');
+
+var $charCodeAt = callBound('String.prototype.charCodeAt');
+var $toUpperCase = callBound('String.prototype.toUpperCase');
+
+var isRegExpRecord = require('../helpers/records/regexp-record');
+var caseFolding = require('../helpers/caseFolding.json');
+
+// https://262.ecma-international.org/14.0/#sec-runtime-semantics-canonicalize-ch
+
+module.exports = function Canonicalize(rer, ch) {
+	if (!isRegExpRecord(rer)) {
+		throw new $TypeError('Assertion failed: `rer` must be a RegExp Record');
+	}
+
+	if (typeof ch !== 'string') {
+		throw new $TypeError('Assertion failed: `ch` must be a character');
+	}
+
+	if (rer['[[Unicode]]'] && rer['[[IgnoreCase]]']) { // step 1
+		if (hasOwn(caseFolding.C, ch)) {
+			return caseFolding.C[ch];
+		}
+		if (hasOwn(caseFolding.S, ch)) {
+			return caseFolding.S[ch];
+		}
+		return ch; // step 1.b
+	}
+
+	if (!rer['[[IgnoreCase]]']) {
+		return ch; // step 2
+	}
+
+	var u = $toUpperCase(ch); // step 5
+
+	if (u.length !== 1) {
+		return ch; // step 7
+	}
+
+	var cu = u; // step 8
+
+	if ($charCodeAt(ch, 0) >= 128 && $charCodeAt(cu, 0) < 128) {
+		return ch; // step 9
+	}
+
+	return cu; // step 10
+};