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/workbox-window/package.json

@@ -0,0 +1,34 @@
+{
+  "name": "workbox-window",
+  "version": "7.4.1",
+  "license": "MIT",
+  "author": "Google's Web DevRel Team and Google's Aurora Team",
+  "description": "Simplifies communications with Workbox packages running in the service worker",
+  "repository": {
+    "type": "git",
+    "url": "git+https://github.com/googlechrome/workbox.git"
+  },
+  "bugs": "https://github.com/googlechrome/workbox/issues",
+  "homepage": "https://github.com/GoogleChrome/workbox",
+  "keywords": [
+    "workbox",
+    "workboxjs",
+    "service worker",
+    "sw",
+    "window",
+    "message",
+    "postMessage"
+  ],
+  "workbox": {
+    "packageType": "window",
+    "primaryBuild": "build/workbox-window.prod.mjs"
+  },
+  "main": "build/workbox-window.prod.umd.js",
+  "module": "build/workbox-window.prod.es5.mjs",
+  "types": "index.d.ts",
+  "dependencies": {
+    "@types/trusted-types": "^2.0.2",
+    "workbox-core": "7.4.1"
+  },
+  "gitHead": "62b9d8ba8eb3c1a2ab8aac9d84c90cda7865d6a3"
+}