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/functions-have-names/index.js

@@ -0,0 +1,31 @@
+'use strict';
+
+var functionsHaveNames = function functionsHaveNames() {
+	return typeof function f() {}.name === 'string';
+};
+
+var gOPD = Object.getOwnPropertyDescriptor;
+if (gOPD) {
+	try {
+		gOPD([], 'length');
+	} catch (e) {
+		// IE 8 has a broken gOPD
+		gOPD = null;
+	}
+}
+
+functionsHaveNames.functionsHaveConfigurableNames = function functionsHaveConfigurableNames() {
+	if (!functionsHaveNames() || !gOPD) {
+		return false;
+	}
+	var desc = gOPD(function () {}, 'name');
+	return !!desc && !!desc.configurable;
+};
+
+var $bind = Function.prototype.bind;
+
+functionsHaveNames.boundFunctionsHaveNames = function boundFunctionsHaveNames() {
+	return functionsHaveNames() && typeof $bind === 'function' && function f() {}.bind().name !== '';
+};
+
+module.exports = functionsHaveNames;