Add explicit validation for server names with multiple slashes

The publish endpoint now validates that server names contain exactly
one forward slash before processing. This provides a clearer error
message (400 Bad Request with "server name cannot contain multiple
slashes") instead of the generic 422 schema validation error.

This fixes test failures where server names like:
- com.example/server/path (2 slashes)
- org.company/dept/team/project (3 slashes)
- com.example//double-slash (consecutive slashes)
- com.example/server/ (trailing slash)

Should now properly return 400 with the expected error message.

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude <[email protected]>

Author: domdomegg

internal/api/handlers/v0/publish.go

@@ -34,6 +34,12 @@ func RegisterPublishEndpoint(api huma.API, registry service.RegistryService, cfg
 			{"bearer": {}},
 		},
 	}, func(ctx context.Context, input *PublishServerInput) (*Response[apiv0.ServerResponse], error) {
+		// Validate server name format (check for multiple slashes before other validations)
+		slashCount := strings.Count(input.Body.Name, "/")
+		if slashCount != 1 {
+			return nil, huma.Error400BadRequest("server name cannot contain multiple slashes")
+		}
+
 		// Extract bearer token
 		const bearerPrefix = "Bearer "
 		authHeader := input.Authorization