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/require-from-string/package.json

@@ -0,0 +1,28 @@
+{
+  "name": "require-from-string",
+  "version": "2.0.2",
+  "description": "Require module from string",
+  "license": "MIT",
+  "repository": "floatdrop/require-from-string",
+  "author": {
+    "name": "Vsevolod Strukchinsky",
+    "email": "floatdrop@gmail.com",
+    "url": "github.com/floatdrop"
+  },
+  "engines": {
+    "node": ">=0.10.0"
+  },
+  "scripts": {
+    "test": "mocha"
+  },
+  "files": [
+    "index.js"
+  ],
+  "keywords": [
+    ""
+  ],
+  "dependencies": {},
+  "devDependencies": {
+    "mocha": "*"
+  }
+}