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/nanoid/url-alphabet/index.cjs

@@ -0,0 +1,4 @@
+let urlAlphabet =
+  'useandom-26T198340PX75pxJACKVERYMINDBUSHWOLF_GQZbfghjklqvwyzrict'
+
+module.exports = { urlAlphabet }

frontend/node_modules/nanoid/url-alphabet/index.js

@@ -0,0 +1,4 @@
+let urlAlphabet =
+  'useandom-26T198340PX75pxJACKVERYMINDBUSHWOLF_GQZbfghjklqvwyzrict'
+
+export { urlAlphabet }

frontend/node_modules/nanoid/url-alphabet/package.json

@@ -0,0 +1,6 @@
+{
+  "type": "module",
+  "main": "index.cjs",
+  "module": "index.js",
+  "react-native": "index.js"
+}