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/react-router/package.json

@@ -0,0 +1,44 @@
+{
+  "name": "react-router",
+  "version": "6.30.4",
+  "description": "Declarative routing for React",
+  "keywords": [
+    "react",
+    "router",
+    "route",
+    "routing",
+    "history",
+    "link"
+  ],
+  "repository": {
+    "type": "git",
+    "url": "https://github.com/remix-run/react-router",
+    "directory": "packages/react-router"
+  },
+  "license": "MIT",
+  "author": "Remix Software <hello@remix.run>",
+  "sideEffects": false,
+  "main": "./dist/main.js",
+  "unpkg": "./dist/umd/react-router.production.min.js",
+  "module": "./dist/index.js",
+  "types": "./dist/index.d.ts",
+  "dependencies": {
+    "@remix-run/router": "1.23.3"
+  },
+  "devDependencies": {
+    "react": "^18.2.0",
+    "react-router-dom": "6.30.4"
+  },
+  "peerDependencies": {
+    "react": ">=16.8"
+  },
+  "files": [
+    "dist/",
+    "CHANGELOG.md",
+    "LICENSE.md",
+    "README.md"
+  ],
+  "engines": {
+    "node": ">=14.0.0"
+  }
+}