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/is-data-view/index.js

@@ -0,0 +1,39 @@
+'use strict';
+
+var GetIntrinsic = require('get-intrinsic');
+
+var $ArrayBuffer = GetIntrinsic('%ArrayBuffer%');
+var $DataView = GetIntrinsic('%DataView%', true);
+
+var callBound = require('call-bound');
+
+// node <= 0.10, < 0.11.4 has a nonconfigurable own property instead of a prototype getter
+var $dataViewBuffer = callBound('DataView.prototype.buffer', true);
+
+var isTypedArray = require('is-typed-array');
+
+/** @type {import('.')} */
+module.exports = function isDataView(x) {
+	if (!x || typeof x !== 'object' || !$DataView || isTypedArray(x)) {
+		return false;
+	}
+
+	if ($dataViewBuffer) {
+		try {
+			$dataViewBuffer(x);
+			return true;
+		} catch (e) {
+			return false;
+		}
+	}
+
+	if (
+		('getInt8' in x)
+			&& typeof x.getInt8 === 'function'
+			&& x.getInt8 === new $DataView(new $ArrayBuffer(1)).getInt8
+	) {
+		return true;
+	}
+
+	return false;
+};