feat: mcp registry

[gregnr]

Adds a server.json registry file + scripts to publish our MCP server to the official MCP registry. For the name field in server.json, opting for the custom domain namespace (com.supabase/*) over GitHub namespace (io.github.supabase-community/mcp-server-supabase) - see namespaces.

Adds:

• server.json
• script to login to the MCP registry (requires feat: mcp registry domain verification supabase/supabase#38561)
• script to update server.json versions to be the same as the package.json version
• NPM script aliases for the above

Note that the MCP registry does not host the servers themselves - just metadata pointing to other registries (like NPM, Docker, etc), or metadata pointing to a remote MCP URL. In this PR we define an NPM stdio entry via packages array in server.json, but in the future when our remote MCP is live we will add it to the remotes array.

Resolve AI-145