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/@trickfilm400/rollup-plugin-off-main-thread/package.json

@@ -0,0 +1,42 @@
+{
+  "name": "@trickfilm400/rollup-plugin-off-main-thread",
+  "version": "3.0.0-pre1",
+  "description": "Use Rollup with workers and ES6 modules today.",
+  "main": "index.js",
+  "scripts": {
+    "fmt": "prettier --write 'tests/**/*.js' *.js *.md *.json",
+    "test": "node ./run_tests.js"
+  },
+  "author": "Surma <surma@google.com>",
+  "contributors": [
+    "trickfilm400 <trickfilm400@gmail.com>"
+  ],
+  "license": "Apache-2.0",
+  "devDependencies": {
+    "chai": "4.5.0",
+    "chalk": "^4.1.2",
+    "karma": "^6.4.4",
+    "karma-chai": "0.1.0",
+    "karma-chrome-launcher": "3.2.0",
+    "karma-firefox-launcher": "^2.1.3",
+    "karma-mocha": "^2.0.1",
+    "karma-safari-launcher": "1.0.0",
+    "karma-safaritechpreview-launcher": "2.0.2",
+    "mocha": "^11.7.5",
+    "prettier": "^3.7.3",
+    "rollup": "^4.53.3"
+  },
+  "repository": {
+    "type": "git",
+    "url": "https://github.com/Trickfilm400/rollup-plugin-off-main-thread"
+  },
+  "dependencies": {
+    "ejs": "^3.1.10",
+    "json5": "^2.2.3",
+    "magic-string": "^0.30.21",
+    "string.prototype.matchall": "^4.0.12"
+  },
+  "engines": {
+    "node": ">=12"
+  }
+}