fix(dashboard): resolve @nous-research/ui path under npm workspaces

The sync-assets prebuild step shelled out to 'cp -r
node_modules/@nous-research/ui/dist/fonts ...' with a path relative
to apps/dashboard/. That works only when the dep is installed
locally in the dashboard workspace, but 'npm install' at the repo
root (the documented setup — see apps/desktop/README.md) hoists
shared deps to the root node_modules under npm workspaces. The
relative cp then fails with 'No such file or directory', sync-assets
exits 1, the Vite build aborts, and 'hermes dashboard' surfaces a
generic 'Web UI build failed' message.

Replace the shell one-liner with scripts/sync-assets.cjs, which
walks up from the dashboard directory looking for node_modules/
@nous-research/ui — working in both the hoisted (workspaces) and
co-located (standalone) layouts. Also guards against a missing
dist/fonts or dist/assets with a clearer error pointing at a
rebuild of the UI package rather than silently copying nothing.

apps/dashboard/package.json

@@ -4,7 +4,7 @@
   "version": "0.0.0",
   "type": "module",
   "scripts": {
-    "sync-assets": "rm -rf public/fonts public/ds-assets && cp -r node_modules/@nous-research/ui/dist/fonts public/fonts && cp -r node_modules/@nous-research/ui/dist/assets public/ds-assets",
+    "sync-assets": "node scripts/sync-assets.cjs",
     "predev": "npm run sync-assets",
     "prebuild": "npm run sync-assets",
     "dev": "vite",