feat: add Go MCP server update API (#15261)

## What

#15240
implementation for PUT /api/v1/mcp/servers/:mcp_id

## Changes

- Adds the Go implementation for `PUT /api/v1/mcp/servers/:mcp_id`.
- Wires MCP service and handler into the Go server/router for the update
route.
- Preserves Python-style behavior for ownership checks, partial update
fields, MCP type/name/URL validation, `headers`/`variables`
normalization, and tool metadata scrubbing.

internal/handler/mcp_test.go

@@ -0,0 +1,71 @@
+//
+//  Copyright 2026 The InfiniFlow Authors. All Rights Reserved.
+//
+//  Licensed under the Apache License, Version 2.0 (the "License");
+//  you may not use this file except in compliance with the License.
+//  You may obtain a copy of the License at
+//
+//      http://www.apache.org/licenses/LICENSE-2.0
+//
+//  Unless required by applicable law or agreed to in writing, software
+//  distributed under the License is distributed on an "AS IS" BASIS,
+//  WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+//  See the License for the specific language governing permissions and
+//  limitations under the License.
+//
+
+package handler
+
+import (
+	"bytes"
+	"encoding/json"
+	"testing"
+	"time"
+
+	"ragflow/internal/entity"
+)
+
+func TestNewMCPServerResponsePreservesNullDescriptionAndFormatsDates(t *testing.T) {
+	createTime := int64(1779949820000)
+	updateTime := int64(1779953420000)
+	location := time.FixedZone("UTC+8", 8*60*60)
+	createDate := time.Date(2026, 5, 28, 10, 30, 20, 0, location)
+	updateDate := time.Date(2026, 5, 28, 11, 30, 20, 0, location)
+
+	response := newMCPServerResponse(&entity.MCPServer{
+		ID:         "mcp-id",
+		Name:       "server",
+		TenantID:   "tenant-id",
+		URL:        "https://example.com/mcp",
+		ServerType: "sse",
+		Variables:  entity.JSONMap{"tools": map[string]interface{}{}},
+		Headers:    entity.JSONMap{"Authorization": "Bearer token"},
+		BaseModel: entity.BaseModel{
+			CreateTime: &createTime,
+			CreateDate: &createDate,
+			UpdateTime: &updateTime,
+			UpdateDate: &updateDate,
+		},
+	})
+
+	if response.Description != nil {
+		t.Fatalf("description = %q, want nil", *response.Description)
+	}
+	if response.CreateDate != "2026-05-28T10:30:20" {
+		t.Fatalf("create_date = %q, want date without timezone", response.CreateDate)
+	}
+	if response.UpdateDate != "2026-05-28T11:30:20" {
+		t.Fatalf("update_date = %q, want date without timezone", response.UpdateDate)
+	}
+
+	payload, err := json.Marshal(response)
+	if err != nil {
+		t.Fatalf("marshal response: %v", err)
+	}
+	if !bytes.Contains(payload, []byte(`"description":null`)) {
+		t.Fatalf("payload %s does not preserve description:null", payload)
+	}
+	if bytes.Contains(payload, []byte(`+08:00`)) {
+		t.Fatalf("payload %s includes timezone in date fields", payload)
+	}
+}