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/caniuse-lite/dist/unpacker/region.js

@@ -0,0 +1,22 @@
+'use strict'
+
+const browsers = require('./browsers').browsers
+
+function unpackRegion(packed) {
+  return Object.keys(packed).reduce((list, browser) => {
+    let data = packed[browser]
+    list[browsers[browser]] = Object.keys(data).reduce((memo, key) => {
+      let stats = data[key]
+      if (key === '_') {
+        stats.split(' ').forEach(version => (memo[version] = null))
+      } else {
+        memo[key] = stats
+      }
+      return memo
+    }, {})
+    return list
+  }, {})
+}
+
+module.exports = unpackRegion
+module.exports.default = unpackRegion