docs: signpost non-npm publishers to package-types from quickstart (#1192)

## What

Two targeted additions to `docs/modelcontextprotocol-io/quickstart.mdx`:

1. A `<Note>` immediately after the tutorial's intro, telling PyPI /
NuGet / OCI / MCPB publishers that the Step 1 ownership-verification
mechanism differs for their package type and pointing them to [Package
Types](./package-types) before continuing.
2. The troubleshooting row for **"Registry validation failed for
package"** previously named only npm's `mcpName` property in
`package.json`. It now names all three current mechanisms (npm →
`mcpName` in `package.json`; PyPI / NuGet → `mcp-name: <server-name>`
line in the package README; other types → link to Package Types).

+5 / -1 lines.

## Why

The quickstart is the landing page for new publishers, but it's entirely
TypeScript / npm-flavored — the Step 1 example shows npm's `mcpName`
property and nothing else. The cross-reference to `./package-types` only
appears in the "Next Steps" footer, by which point a PyPI publisher has
already gone through every step and hit a `400 Bad Request` at
`mcp-publisher publish`:

> `registry validation failed for package 0 (<pkg>): PyPI package
'<pkg>' ownership validation failed. The server name
'io.github.<user>/<server>' must appear as 'mcp-name:
io.github.<user>/<server>' in the package README`

That specific error has tripped at least one other publisher (#531) and
was what motivated this change. The ownership mechanism is correctly
documented at `./package-types` — the fix is purely to route people
there before they publish, not to duplicate the content.

## What this change is **not**

- It does not propose changing the validation logic.
- It does not duplicate content from `package-types.mdx` into the
quickstart.
- It does not add a separate PyPI-specific tutorial. The existing
npm-flavored tutorial remains the canonical one; the note just tells
non-npm readers which step is different.

## Verification

- Change is docs-only; no build or test impact.
- Link target `./package-types` is the same shape as the one already
used in "Next Steps" of the same file.
- Anchor `#step-1-add-verification-information-to-the-package` matches
the existing heading's slug.

## Related

- #531 — same validation error hit by another PyPI publisher; closed
with a workaround but the quickstart wasn't updated.

docs/modelcontextprotocol-io/quickstart.mdx

@@ -9,6 +9,10 @@ sidebarTitle: "Quickstart: Publish a Server"
 
 This tutorial will show you how to publish an MCP server written in TypeScript to the MCP Registry using the official `mcp-publisher` CLI tool.
 
+<Note>
+  If you are publishing a non-npm package (PyPI, NuGet, OCI, MCPB), the overall flow is identical, but the ownership-verification step in [Step 1](#step-1-add-verification-information-to-the-package) is different per package type. See [Package Types](./package-types) for the verification mechanism that applies to your package, then return here and follow the remaining steps.
+</Note>
+
 ## Prerequisites
 
 - **Node.js** — This tutorial assumes the MCP server is written in TypeScript.
@@ -279,7 +283,7 @@ You should see your server's metadata in the search results JSON:
 
 | Error Message | Action |
 | --- | --- |
-|"Registry validation failed for package"|Ensure your package includes the required validation information (e.g, `mcpName` property in `package.json`).|
+|"Registry validation failed for package"|Ensure your package includes the required ownership-verification marker for its package type. For npm this is `mcpName` in `package.json`; for PyPI and NuGet it is an `mcp-name: <server-name>` line (or HTML comment) in the package README; for other types see [Package Types](./package-types).|
 |"Invalid or expired Registry JWT token"|Re-authenticate by running `mcp-publisher login github`.|
 |"You do not have permission to publish this server"|Your authentication method doesn't match your server's namespace format. With GitHub auth, your server name must start with `io.github.your-username/`.|