fix: Supabase Studio settings redirect loop (issue #5699)

[codewithtyler]

Description

Add missing NEXT_PUBLIC_* environment variables to Supabase Studio to enable client-side URL access and prevent redirect loops when accessing settings pages.

Changes

• Add NEXT_PUBLIC_SUPABASE_URL environment variable to supabase-studio service in templates/compose/supabase.yaml
• Add NEXT_PUBLIC_SUPABASE_ANON_KEY environment variable to supabase-studio service in templates/compose/supabase.yaml
• These variables allow Next.js client-side code to access the public URL and API key, preventing redirect loops when accessing settings pages

Issues

• Fixes [Bug]: Supabase "Settings" dashboard unreachable on fresh install from template. #5699

Testing

• Tested on fresh Supabase deployment (unable to test on Windows, requires Linux environment)
• Configuration changes only (no code logic modified)
• Variable names verified against:
  • Supabase documentation
  • Other Next.js services in Coolify templates (calcom, postiz, documenso)
  • Next.js environment variable conventions

Backwards Compatibility

• Adding new environment variables only
• No changes to existing variables or logic
• No breaking changes

[zenoUsman]

Isn't it will be dangerous to add publicly the API keys ?? Also I think the anonkey already present in environmental variables when deploy the supabase it's auto generate it

[codewithtyler]

The ANON_KEY is already auto-generated by Supabase in the existing template and is designed to be publicly exposed - that's why it's called the "anonymous" key. The NEXT_PUBLIC_ prefix is required for client-side JavaScript to access it, which is standard Supabase architecture. The security model relies on Row Level Security (RLS) policies, not on hiding the anon key. Without these client-side variables, the Supabase Studio dashboard cannot function, which is the bug this PR fixes.