docs(swagger): fix response type annotations for swagger generation

Update DeleteMasterKey endpoint to use MapData instead of dto.DeleteResponse
and add blank references for model registry DTOs to ensure proper swagger
documentation generation.

internal/api/model_registry_handler.go

@@ -4,10 +4,17 @@ import (
 	"net/http"
 	"strings"
 
+	"github.com/ez-api/ez-api/internal/dto"
 	"github.com/ez-api/ez-api/internal/service"
 	"github.com/gin-gonic/gin"
 )
 
+// Blank references for swagger doc generation
+var (
+	_ dto.ModelRegistryStatusResponse
+	_ dto.ModelRegistryCheckResponse
+)
+
 type ModelRegistryHandler struct {
 	reg *service.ModelRegistryService
 }