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/rollup/dist/es/rollup.js

@@ -0,0 +1,17 @@
+/*
+  @license
+	Rollup.js v4.62.2
+	Fri, 19 Jun 2026 14:55:11 GMT - commit 8faa18777374582bb813d54ce3623f4acf1f9e0b
+
+	https://github.com/rollup/rollup
+
+	Released under the MIT License.
+*/
+export { VERSION, defineConfig, rollup, watch } from './shared/node-entry.js';
+import './shared/parseAst.js';
+import '../native.js';
+import 'node:path';
+import 'path';
+import 'node:process';
+import 'node:perf_hooks';
+import 'node:fs/promises';