feat(go-api): migrate MCP server detail and download API to Go (#16113)

### What problem does this PR solve?

- Migrated MCP server detail and export (download) API from Python to
Go.
- Registered route: `GET /api/v1/mcp/servers/:mcp_id` (supporting
`?mode=download` query parameter).

internal/handler/mcp.go

@@ -139,6 +139,56 @@ func (h *MCPHandler) ListMCPServers(c *gin.Context) {
 	})
 }
 
+func (h *MCPHandler) GetMCPServer(c *gin.Context) {
+	user, errorCode, errorMessage := GetUser(c)
+	if errorCode != common.CodeSuccess {
+		jsonError(c, errorCode, errorMessage)
+		return
+	}
+
+	mcpID := c.Param("mcp_id")
+	if c.Query("mode") == "download" {
+		result, code, err := h.mcpService.ExportMCPServer(user.ID, mcpID)
+		if err != nil {
+			mcpDetailError(c, code, err)
+			return
+		}
+		c.JSON(http.StatusOK, gin.H{
+			"code":    common.CodeSuccess,
+			"message": "success",
+			"data":    result,
+		})
+		return
+	}
+
+	result, code, err := h.mcpService.GetMCPServer(user.ID, mcpID)
+	if err != nil {
+		mcpDetailError(c, code, err)
+		return
+	}
+	c.JSON(http.StatusOK, gin.H{
+		"code":    common.CodeSuccess,
+		"message": "success",
+		"data":    newMCPServerResponse(result),
+	})
+}
+
+func mcpDetailError(c *gin.Context, code common.ErrorCode, err error) {
+	if code == common.CodeDataError {
+		c.JSON(http.StatusOK, gin.H{
+			"code":    code,
+			"message": err.Error(),
+		})
+		return
+	}
+	c.JSON(http.StatusOK, gin.H{
+		"code":    common.CodeExceptionError,
+		"message": err.Error(),
+		"data":    nil,
+	})
+}
+
+
 // UpdateMCPServer updates an MCP server for the current user.
 func (h *MCPHandler) UpdateMCPServer(c *gin.Context) {
 	user, errorCode, errorMessage := GetUser(c)

internal/handler/mcp_test.go

@@ -19,9 +19,15 @@ package handler
 import (
 	"bytes"
 	"encoding/json"
+	"errors"
+	"net/http"
+	"net/http/httptest"
 	"testing"
 	"time"
 
+	"github.com/gin-gonic/gin"
+
+	"ragflow/internal/common"
 	"ragflow/internal/entity"
 )
 
@@ -69,3 +75,28 @@ func TestNewMCPServerResponsePreservesNullDescriptionAndFormatsDates(t *testing.
 		t.Fatalf("payload %s includes timezone in date fields", payload)
 	}
 }
+
+func TestMCPDetailDataErrorOmitsDataFieldLikePython(t *testing.T) {
+	gin.SetMode(gin.TestMode)
+	recorder := httptest.NewRecorder()
+	c, _ := gin.CreateTestContext(recorder)
+
+	mcpDetailError(c, common.CodeDataError, errors.New("Cannot find MCP server mcp-id for user user-id"))
+
+	if recorder.Code != http.StatusOK {
+		t.Fatalf("status = %d, want %d", recorder.Code, http.StatusOK)
+	}
+	var body map[string]interface{}
+	if err := json.Unmarshal(recorder.Body.Bytes(), &body); err != nil {
+		t.Fatalf("unmarshal body: %v", err)
+	}
+	if body["code"] != float64(common.CodeDataError) {
+		t.Fatalf("code = %v, want %d", body["code"], common.CodeDataError)
+	}
+	if body["message"] != "Cannot find MCP server mcp-id for user user-id" {
+		t.Fatalf("message = %v", body["message"])
+	}
+	if _, ok := body["data"]; ok {
+		t.Fatalf("body unexpectedly contains data field: %s", recorder.Body.String())
+	}
+}