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/data-view-byte-length/test/index.js

@@ -0,0 +1,31 @@
+'use strict';
+
+var test = require('tape');
+var forEach = require('for-each');
+var v = require('es-value-fixtures');
+var inspect = require('object-inspect');
+
+var dataViewByteLength = require('../');
+
+test('dataViewByteLength', function (t) {
+	forEach(
+		// @ts-expect-error TS sucks at [].concat
+		// eslint-disable-next-line no-extra-parens
+		/** @type {[...typeof v.primitives, ...typeof v.objects]} */ ([].concat(v.primitives, v.objects)),
+		function (nonDV) {
+			t['throws'](function () { dataViewByteLength(nonDV); }, TypeError, inspect(nonDV) + ' is not a DataView');
+		}
+	);
+
+	t.test('DataView', { skip: typeof DataView !== 'function' }, function (st) {
+		var ab = new ArrayBuffer(42);
+		var dv = new DataView(ab);
+
+		st.equal(dataViewByteLength(dv), 42, inspect(dv) + ' has the same byteLength as the buffer originally passed to the DataView');
+		st.equal(dataViewByteLength(dv), dv.buffer.byteLength, inspect(dv) + ' has the same byteLength as the buffer’s byteLength of its own buffer property');
+
+		st.end();
+	});
+
+	t.end();
+});