Claim a custom-domain namespace in the MCP Registry with HTTP well-known authentication

Documented steps

1. Use this instead of DNS TXT when you can deploy files to the domain faster than you can change DNS. It grants the same com.example.*/* namespace. Ref: https://modelcontextprotocol.io/registry/authentication
2. Generate a key pair: `openssl genpkey -algorithm Ed25519 -out key.pem` (or EC secp384r1 for P-384).
3. Create the proof file: PUBLIC_KEY="$(openssl pkey -in key.pem -pubout -outform DER | tail -c 32 | base64)"; echo "v=MCPv1; k=ed25519; p=${PUBLIC_KEY}" > mcp-registry-auth
4. Host it at exactly https://example.com/.well-known/mcp-registry-auth and confirm with `curl -sS https://example.com/.well-known/mcp-registry-auth` that the raw line is returned.
5. Log in: PRIVATE_KEY="$(openssl pkey -in key.pem -noout -text | grep -A3 "priv:" | tail -n +2 | tr -d ' :\n')"; `mcp-publisher login http --domain "example.com" --private-key "${PRIVATE_KEY}"`.
6. KMS variants exist: `mcp-publisher login http google-kms --domain=... --resource=...` and `mcp-publisher login http azure-key-vault --domain=... --vault ... --key ...`; run once to print the expected proof line to host.
7. Set server.json `name` to the reverse-DNS namespace and publish.