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/2025/ToUint8Clamp.js

@@ -0,0 +1,26 @@
+'use strict';
+
+var clamp = require('./clamp');
+
+var ToNumber = require('./ToNumber');
+var floor = require('./floor');
+
+var $isNaN = require('math-intrinsics/isNaN');
+
+// https://262.ecma-international.org/15.0/#sec-touint8clamp
+
+module.exports = function ToUint8Clamp(argument) {
+	var number = ToNumber(argument); // step 1
+
+	if ($isNaN(number)) { return 0; } // step 2
+
+	var clamped = clamp(number, 0, 255); // step 4
+
+	var f = floor(clamped); // step 5
+
+	if (clamped < (f + 0.5)) { return f; } // step 6
+
+	if (clamped > (f + 0.5)) { return f + 1; } // step 7
+
+	return f % 2 === 0 ? f : f + 1; // step 8
+};