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-shared-array-buffer/test/index.js

@@ -0,0 +1,39 @@
+'use strict';
+
+var test = require('tape');
+var inspect = require('object-inspect');
+var forEach = require('for-each');
+var v = require('es-value-fixtures');
+var availableTypedArrays = require('available-typed-arrays')();
+
+var isSharedArrayBuffer = require('..');
+
+test('isSharedArrayBuffer', function (t) {
+	t.equal(typeof isSharedArrayBuffer, 'function', 'is a function');
+
+	// @ts-expect-error TS sucks with concat
+	var nonSABs = [].concat(v.primitives, v.objects);
+	forEach(nonSABs, function (nonSAB) {
+		t.equal(isSharedArrayBuffer(nonSAB), false, inspect(nonSAB) + ' is not a SharedArrayBuffer');
+	});
+
+	t.test('actual SharedArrayBuffer instances', { skip: typeof SharedArrayBuffer === 'undefined' }, function (st) {
+		var sab = new SharedArrayBuffer(0);
+
+		st.equal(isSharedArrayBuffer(sab), true, inspect(sab) + ' is a SharedArrayBuffer');
+
+		st.end();
+	});
+
+	t.test('Typed Arrays', { skip: availableTypedArrays.length === 0 }, function (st) {
+		forEach(availableTypedArrays, function (TypedArray) {
+			var ta = new global[TypedArray](0);
+			st.equal(isSharedArrayBuffer(ta.buffer), false, inspect(ta.buffer) + ', the TA\'s buffer, is not a SharedArrayBuffer');
+			st.equal(isSharedArrayBuffer(ta), false, inspect(ta) + ' is not a SharedArrayBuffer');
+		});
+
+		st.end();
+	});
+
+	t.end();
+});