Add NEXT_PUBLIC_CONVEX_URL and NEXT_PUBLIC_CONVEX_SITE_URL to .env.example. Add !.env.example exception to .gitignore so template env file is tracked.
Ultraworked with [Sisyphus](https://github.com/code-yeongyu/oh-my-openagent)
Co-authored-by: Sisyphus <clio-agent@sisyphuslabs.ai>
