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/lodash.debounce/package.json

@@ -0,0 +1,17 @@
+{
+  "name": "lodash.debounce",
+  "version": "4.0.8",
+  "description": "The lodash method `_.debounce` exported as a module.",
+  "homepage": "https://lodash.com/",
+  "icon": "https://lodash.com/icon.svg",
+  "license": "MIT",
+  "keywords": "lodash-modularized, debounce",
+  "author": "John-David Dalton <john.david.dalton@gmail.com> (http://allyoucanleet.com/)",
+  "contributors": [
+    "John-David Dalton <john.david.dalton@gmail.com> (http://allyoucanleet.com/)",
+    "Blaine Bublitz <blaine.bublitz@gmail.com> (https://github.com/phated)",
+    "Mathias Bynens <mathias@qiwi.be> (https://mathiasbynens.be/)"
+  ],
+  "repository": "lodash/lodash",
+  "scripts": { "test": "echo \"See https://travis-ci.org/lodash/lodash-cli for testing details.\"" }
+}