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/2016/AbstractEqualityComparison.js

@@ -0,0 +1,38 @@
+'use strict';
+
+var ToNumber = require('./ToNumber');
+var ToPrimitive = require('./ToPrimitive');
+
+var isSameType = require('../helpers/isSameType');
+
+var isObject = require('es-object-atoms/isObject');
+
+// https://262.ecma-international.org/6.0/#sec-abstract-equality-comparison
+
+module.exports = function AbstractEqualityComparison(x, y) {
+	if (isSameType(x, y)) {
+		return x === y; // ES6+ specified this shortcut anyways.
+	}
+	if (x == null && y == null) {
+		return true;
+	}
+	if (typeof x === 'number' && typeof y === 'string') {
+		return AbstractEqualityComparison(x, ToNumber(y));
+	}
+	if (typeof x === 'string' && typeof y === 'number') {
+		return AbstractEqualityComparison(ToNumber(x), y);
+	}
+	if (typeof x === 'boolean') {
+		return AbstractEqualityComparison(ToNumber(x), y);
+	}
+	if (typeof y === 'boolean') {
+		return AbstractEqualityComparison(x, ToNumber(y));
+	}
+	if ((typeof x === 'string' || typeof x === 'number' || typeof x === 'symbol') && isObject(y)) {
+		return AbstractEqualityComparison(x, ToPrimitive(y));
+	}
+	if (isObject(x) && (typeof y === 'string' || typeof y === 'number' || typeof y === 'symbol')) {
+		return AbstractEqualityComparison(ToPrimitive(x), y);
+	}
+	return false;
+};