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/StringPaddingBuiltinsImpl.js

@@ -0,0 +1,27 @@
+'use strict';
+
+var $TypeError = require('es-errors/type');
+
+var StringPad = require('./StringPad');
+var ToLength = require('./ToLength');
+var ToString = require('./ToString');
+
+// https://262.ecma-international.org/15.0/#sec-stringpaddingbuiltinsimpl
+
+module.exports = function StringPaddingBuiltinsImpl(O, maxLength, fillString, placement) {
+	if (placement !== 'start' && placement !== 'end' && placement !== 'START' && placement !== 'END') {
+		throw new $TypeError('Assertion failed: `placement` must be ~START~ or ~END~');
+	}
+
+	var S = ToString(O); // step 1
+
+	var intMaxLength = ToLength(maxLength); // step 2
+
+	var stringLength = S.length; // step 3
+
+	if (intMaxLength <= stringLength) { return S; } // step 4
+
+	var filler = typeof fillString === 'undefined' ? ' ' : ToString(fillString); // steps 5-6
+
+	return StringPad(S, intMaxLength, filler, placement); // step 7
+};