feat(group): 添加 MCP XML 注入开关

- Group 新增 mcp_xml_inject 字段，控制 Antigravity 平台的 MCP XML 协议注入
- 默认启用，可在分组设置中关闭
- 修复 GetByKeyForAuth 遗漏查询 mcp_xml_inject 字段导致认证缓存值始终为 false 的问题

backend/internal/handler/admin/group_handler.go

@@ -44,6 +44,7 @@ type CreateGroupRequest struct {
 	// 模型路由配置（仅 anthropic 平台使用）
 	ModelRouting        map[string][]int64 `json:"model_routing"`
 	ModelRoutingEnabled bool               `json:"model_routing_enabled"`
+	MCPXMLInject        *bool              `json:"mcp_xml_inject"`
 }
 
 // UpdateGroupRequest represents update group request
@@ -68,6 +69,7 @@ type UpdateGroupRequest struct {
 	// 模型路由配置（仅 anthropic 平台使用）
 	ModelRouting        map[string][]int64 `json:"model_routing"`
 	ModelRoutingEnabled *bool              `json:"model_routing_enabled"`
+	MCPXMLInject        *bool              `json:"mcp_xml_inject"`
 }
 
 // List handles listing all groups with pagination
@@ -174,6 +176,7 @@ func (h *GroupHandler) Create(c *gin.Context) {
 		FallbackGroupIDOnInvalidRequest: req.FallbackGroupIDOnInvalidRequest,
 		ModelRouting:                    req.ModelRouting,
 		ModelRoutingEnabled:             req.ModelRoutingEnabled,
+		MCPXMLInject:                    req.MCPXMLInject,
 	})
 	if err != nil {
 		response.ErrorFrom(c, err)
@@ -217,6 +220,7 @@ func (h *GroupHandler) Update(c *gin.Context) {
 		FallbackGroupIDOnInvalidRequest: req.FallbackGroupIDOnInvalidRequest,
 		ModelRouting:                    req.ModelRouting,
 		ModelRoutingEnabled:             req.ModelRoutingEnabled,
+		MCPXMLInject:                    req.MCPXMLInject,
 	})
 	if err != nil {
 		response.ErrorFrom(c, err)

backend/internal/handler/dto/mappers.go

@@ -92,6 +92,7 @@ func GroupFromServiceShallow(g *service.Group) *Group {
 		FallbackGroupIDOnInvalidRequest: g.FallbackGroupIDOnInvalidRequest,
 		ModelRouting:                    g.ModelRouting,
 		ModelRoutingEnabled:             g.ModelRoutingEnabled,
+		MCPXMLInject:                    g.MCPXMLInject,
 		CreatedAt:                       g.CreatedAt,
 		UpdatedAt:                       g.UpdatedAt,
 		AccountCount:                    g.AccountCount,

backend/internal/handler/dto/types.go

@@ -69,6 +69,9 @@ type Group struct {
 	ModelRouting        map[string][]int64 `json:"model_routing"`
 	ModelRoutingEnabled bool               `json:"model_routing_enabled"`
 
+	// MCP XML 协议注入（仅 antigravity 平台使用）
+	MCPXMLInject bool `json:"mcp_xml_inject"`
+
 	CreatedAt time.Time `json:"created_at"`
 	UpdatedAt time.Time `json:"updated_at"`