Implement Service Discovery Protocol

We need to implement the service discovery protocol endpoint as per the Registry API spec at /.well-known/terraform.json

Tasks:
- Implement /.well-known/terraform.json endpoint
- Return proper modules.v1 base URL with trailing slash
- Ensure all module URLs are relative to this base URL
- Update nginx config to route this endpoint correctly

Required Response should return modules.v1 with /v1/modules/ value

Start with the Registry API specification for /.well-known/terraform.json and inspect the repository's nginx configuration. Verify the endpoint returns modules.v1 with a trailing-slash base URL and that module URLs are relative to it, then confirm nginx routes the endpoint correctly.

Written by the indexing model from the issue text.