ci: publish releases to the official MCP Registry

[denial123789]

Summary

• add the official GitHub OIDC publishing flow for the MCP Registry
• validate that the selected npm package exists and carries the expected mcpName
• support both published releases and an explicit manual version
• verify the published Registry entry after submission

This follows the MCP Registry official GitHub Actions guidance and requires no new secret.

Disclosure: I am affiliated with SandBase, and this change was prepared with AI assistance.