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/reference/api/CHANGELOG.md

@@ -2,6 +2,17 @@
 
 Changes to the REST API endpoints and responses.
 
+## Unreleased
+
+### ⚠️ BREAKING CHANGES
+
+#### Endpoint Simplification
+
+Removed redundant endpoint to simplify API surface and reduce implementation burden for subregistries.
+
+**Removed endpoints:**
+- `GET /v0/servers/{serverName}` - Use `GET /v0/servers/{serverName}/versions/latest` instead
+
 ## 2025-09-29
 
 ### ⚠️ BREAKING CHANGES