chore(server): Add public/ to .gitignore (build artifacts)

Agent-Logs-Url: https://github.com/objectstack-ai/framework/sessions/38859349-2ac2-4ed9-a6ab-dc857bf07fba

Co-authored-by: hotlong <50353452+hotlong@users.noreply.github.com>

Author: Claude

apps/server/.gitignore

@@ -1,6 +1,7 @@
 # Build artifacts
 dist/
 .turbo/
+public/
 
 # Bundled API handler (generated during Vercel build)
 api/_handler.js