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/fast-uri/benchmark/non-simple-domain.mjs

@@ -0,0 +1,22 @@
+import { Bench } from 'tinybench'
+import { nonSimpleDomain } from '../lib/utils.js'
+
+const benchNonSimpleDomain = new Bench({ name: 'nonSimpleDomain' })
+
+const exampleCom = 'example.com'
+const exaumlmpleCom = 'exämple.com'
+const longDomain = 'abc'.repeat(100) + '.com'
+
+console.assert(nonSimpleDomain(exampleCom) === false, 'example.com should be a simple domain')
+console.assert(nonSimpleDomain(exaumlmpleCom) === true, 'exämple.com should not be a simple domain')
+console.assert(nonSimpleDomain(longDomain) === false, `${longDomain} should be a simple domain?`)
+
+benchNonSimpleDomain.add('nonSimpleDomain', function () {
+  nonSimpleDomain(exampleCom)
+  nonSimpleDomain(exaumlmpleCom)
+  nonSimpleDomain(longDomain)
+})
+
+await benchNonSimpleDomain.run()
+console.log(benchNonSimpleDomain.name)
+console.table(benchNonSimpleDomain.table())