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/browserslist/package.json

@@ -0,0 +1,45 @@
+{
+  "name": "browserslist",
+  "version": "4.28.5",
+  "description": "Share target browsers between different front-end tools, like Autoprefixer, Stylelint and babel-env-preset",
+  "keywords": [
+    "browsers",
+    "caniuse",
+    "target"
+  ],
+  "license": "MIT",
+  "author": "Andrey Sitnik <andrey@sitnik.es>",
+  "repository": "browserslist/browserslist",
+  "funding": [
+    {
+      "type": "opencollective",
+      "url": "https://opencollective.com/browserslist"
+    },
+    {
+      "type": "tidelift",
+      "url": "https://tidelift.com/funding/github/npm/browserslist"
+    },
+    {
+      "type": "github",
+      "url": "https://github.com/sponsors/ai"
+    }
+  ],
+  "bin": {
+    "browserslist": "cli.js"
+  },
+  "browser": {
+    "./node.js": "./browser.js",
+    "path": false
+  },
+  "types": "./index.d.ts",
+  "dependencies": {
+    "baseline-browser-mapping": "^2.10.42",
+    "caniuse-lite": "^1.0.30001800",
+    "electron-to-chromium": "^1.5.387",
+    "node-releases": "^2.0.50",
+    "update-browserslist-db": "^1.2.3"
+  },
+  "engines": {
+    "node": "^6 || ^7 || ^8 || ^9 || ^10 || ^11 || ^12 || >=13.7"
+  }
+}