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/2022/Number/index.js

@@ -0,0 +1,43 @@
+'use strict';
+
+var add = require('./add');
+var bitwiseAND = require('./bitwiseAND');
+var bitwiseNOT = require('./bitwiseNOT');
+var bitwiseOR = require('./bitwiseOR');
+var bitwiseXOR = require('./bitwiseXOR');
+var divide = require('./divide');
+var equal = require('./equal');
+var exponentiate = require('./exponentiate');
+var leftShift = require('./leftShift');
+var lessThan = require('./lessThan');
+var multiply = require('./multiply');
+var remainder = require('./remainder');
+var sameValue = require('./sameValue');
+var sameValueZero = require('./sameValueZero');
+var signedRightShift = require('./signedRightShift');
+var subtract = require('./subtract');
+var toString = require('./toString');
+var unaryMinus = require('./unaryMinus');
+var unsignedRightShift = require('./unsignedRightShift');
+
+module.exports = {
+	add: add,
+	bitwiseAND: bitwiseAND,
+	bitwiseNOT: bitwiseNOT,
+	bitwiseOR: bitwiseOR,
+	bitwiseXOR: bitwiseXOR,
+	divide: divide,
+	equal: equal,
+	exponentiate: exponentiate,
+	leftShift: leftShift,
+	lessThan: lessThan,
+	multiply: multiply,
+	remainder: remainder,
+	sameValue: sameValue,
+	sameValueZero: sameValueZero,
+	signedRightShift: signedRightShift,
+	subtract: subtract,
+	toString: toString,
+	unaryMinus: unaryMinus,
+	unsignedRightShift: unsignedRightShift
+};