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/2024/MakeTime.js

@@ -0,0 +1,23 @@
+'use strict';
+
+var $isFinite = require('math-intrinsics/isFinite');
+var timeConstants = require('../helpers/timeConstants');
+var msPerSecond = timeConstants.msPerSecond;
+var msPerMinute = timeConstants.msPerMinute;
+var msPerHour = timeConstants.msPerHour;
+
+var ToIntegerOrInfinity = require('./ToIntegerOrInfinity');
+
+// https://262.ecma-international.org/12.0/#sec-maketime
+
+module.exports = function MakeTime(hour, min, sec, ms) {
+	if (!$isFinite(hour) || !$isFinite(min) || !$isFinite(sec) || !$isFinite(ms)) {
+		return NaN;
+	}
+	var h = ToIntegerOrInfinity(hour);
+	var m = ToIntegerOrInfinity(min);
+	var s = ToIntegerOrInfinity(sec);
+	var milli = ToIntegerOrInfinity(ms);
+	var t = (h * msPerHour) + (m * msPerMinute) + (s * msPerSecond) + milli;
+	return t;
+};