Drop GET /v0/servers/{serverName} endpoint (#618)

Remove redundant endpoint as suggested in #617. Clients should now use
`GET /v0/servers/{serverName}/versions/latest` instead (using `latest`
as a special version value in the existing endpoint).

This simplifies the API surface and reduces implementation burden for
subregistries, while maintaining a clear migration path for consumers.

## Changes
- Removed `GET /v0/servers/{serverName}` endpoint
- Updated `GET /v0/servers/{serverName}/versions/{version}` to accept
`latest` as special version
- Updated all tests to use new endpoint pattern
- Updated documentation and OpenAPI spec
- Added breaking change notice to CHANGELOG

Fixes #617

Co-authored-by: Claude <noreply@anthropic.com>

docs/guides/consuming/use-rest-api.md

@@ -9,9 +9,10 @@ Integration patterns and best practices for building applications that consume M
 **Authentication**: Not required for read-only access
 
 - **`GET /v0/servers`** - List all servers with pagination
-- **`GET /v0/servers/{serverName}`** - Get latest version of server by server name (URL-encoded)
-- **`GET /v0/servers/{serverName}/versions/{version}`** - Get specific version of server
 - **`GET /v0/servers/{serverName}/versions`** - List all versions of a server
+- **`GET /v0/servers/{serverName}/versions/{version}`** - Get specific version of server. Use the special version `latest` to get the latest version.
+
+Server names and version strings should be URL-encoded in paths.
 
 See the [interactive API documentation](https://registry.modelcontextprotocol.io/docs) for complete request/response schemas.