Consider `/.wk/mcp-registry-auth` => `/.wk/mcp/registry-auth`

[jonathanhefner]

(Not really sure if this is a GA blocker, but wanted to raise attention, just in case.)

The MCP Registry currently uses /.well-known/mcp-registry-auth for DNS-based auth:

https://github.com/modelcontextprotocol/registry/blob/68213d2befd88e887688cedad74636208c078f0d/docs/explanations/namespacing.md?plain=1#L26

However, there is a desire to support /.well-known/mcp/server.json. For example, see https://github.com/modelcontextprotocol/modelcontextprotocol/issues/1649.

So should we change /.well-known/mcp-registry-auth to /.well-known/mcp/registry-auth?