Docs: add a Go stdio publishing example for OCI or MCPB packages

Summary

The current publishing quickstart is very npm/TypeScript-oriented, and package-types.mdx explains the supported registries, but there is still a gap for Go-based stdio servers that want to publish through OCI or MCPB.

I hit this while trying to publish embercore, a Go MCP server, to the registry.

Problem

Today the docs make it clear that non-npm package types are supported, but there is not a concrete end-to-end example for a Go server that ships as:

• an OCI image (for registryType: "oci"), or
• an MCPB artifact attached to a GitHub release

That leaves a few practical questions unanswered for Go maintainers:

• what the recommended path is for a stdio Go server without an npm package
• what a minimal server.json should look like for OCI vs MCPB
• how ownership verification is expected to work in a typical Go release workflow
• what the simplest CI/release path looks like

Proposed improvement

Add a short Go-oriented publishing guide (or extend the existing quickstart) that shows one concrete path, for example:

1. build a Go stdio server binary
2. package it as an OCI image or MCPB artifact
3. add the required registry metadata
4. publish with mcp-publisher
5. verify the listing via the registry API

Even a minimal example repo or a docs snippet would remove a lot of ambiguity for Go SDK users.

Why this helps more than one project

This would help maintainers building on mcp-go and similar SDKs, not just a single server. The registry already supports these package types, so a concrete guide seems like a high-leverage documentation improvement.

Start with the current publishing quickstart and package-types.mdx, then trace the documented mcp-publisher and registry API workflow. Add a concise Go stdio example covering either OCI or MCPB packaging, registry metadata, ownership verification, publishing, and verification of the resulting listing.