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/unicode-canonical-property-names-ecmascript/package.json

@@ -0,0 +1,34 @@
+{
+  "name": "unicode-canonical-property-names-ecmascript",
+  "version": "2.0.1",
+  "description": "The set of canonical Unicode property names supported in ECMAScript RegExp property escapes.",
+  "homepage": "https://github.com/mathiasbynens/unicode-canonical-property-names-ecmascript",
+  "main": "index.js",
+  "engines": {
+    "node": ">=4"
+  },
+  "files": [
+    "LICENSE-MIT.txt",
+    "index.js"
+  ],
+  "keywords": [
+    "unicode",
+    "unicode properties"
+  ],
+  "license": "MIT",
+  "author": {
+    "name": "Mathias Bynens",
+    "url": "https://mathiasbynens.be/"
+  },
+  "repository": {
+    "type": "git",
+    "url": "https://github.com/mathiasbynens/unicode-canonical-property-names-ecmascript.git"
+  },
+  "bugs": "https://github.com/mathiasbynens/unicode-canonical-property-names-ecmascript/issues",
+  "devDependencies": {
+    "ava": "*"
+  },
+  "scripts": {
+    "test": "ava tests/tests.js"
+  }
+}