fix(app-host): remove .npmrc to fix Vercel pnpm install conflict

The app-host/.npmrc with node-linker=hoisted was causing pnpm install
conflicts on Vercel (ERR_PNPM_EEXIST). Studio doesn't have a local .npmrc
and works fine, so removing it to match that pattern.

Agent-Logs-Url: https://github.com/objectstack-ai/framework/sessions/9f2af2b5-3ebb-470a-944d-918293a36a82

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

Author: Claude