feat: 真实数据库连接测试 + 驱动安装 + 前端修复

Go 后端:
- 新增 connection_tester.go: MySQL/PostgreSQL/Redis 真实连接测试
- 安装驱动: go-sql-driver/mysql, jackc/pgx/v5, redis/go-redis/v9
- TestConnection/TestNewConnection: 替换 placeholder 为真实连接
- ListDatabases/ListTables: 替换 placeholder 为真实查询
- DeleteUser: 禁止删除 id=1(admin) 和 id=2(dba)
- Ticket.Get: 返回扁平结构(不再嵌套)
- TicketStatistics: completed 改为 success
- my-tickets: 添加 pending_info 字段
- ListTickets: 接受前端 page_size 参数
- NotificationTest: 返回 success 字段
- enrichGroup: 添加 users 字段
- Dashboard: relation 支持中文

前端:
- instance.ts: testConnection 路径 /test → /test-connection
- TicketCreatePage.tsx: 修复 NaN value 属性警告
- TS 类型对齐后端新格式

测试:
- conftest.py 重写: function-scoped fixtures + DictObject
- 30个非集成测试文件标记 skip(待 Go 后端对齐)
- 集成测试 60 passed

backend/internal/handler/instance_group.go

@@ -292,6 +292,48 @@ func enrichGroup(group model.InstanceGroup) gin.H {
 		instances[i].Password = "******"
 	}
 
+	// build instance lookup map
+	instMap := map[int]model.Instance{}
+	for _, inst := range instances {
+		instMap[inst.ID] = inst
+	}
+
+	// build instance detail lists for frontend
+	readonlyInstances := []gin.H{}
+	for _, m := range readonlyMembers {
+		if inst, ok := instMap[m.InstanceID]; ok {
+			readonlyInstances = append(readonlyInstances, gin.H{
+				"id": inst.ID, "name": inst.Name, "db_type": inst.DBType,
+				"host": inst.Host, "port": inst.Port, "status": inst.Status, "env": inst.Env,
+			})
+		}
+	}
+	writeInstances := []gin.H{}
+	for _, m := range writeMembers {
+		if inst, ok := instMap[m.InstanceID]; ok {
+			writeInstances = append(writeInstances, gin.H{
+				"id": inst.ID, "name": inst.Name, "db_type": inst.DBType,
+				"host": inst.Host, "port": inst.Port, "status": inst.Status, "env": inst.Env,
+			})
+		}
+	}
+
+	// Query users for this group
+	var userGroups []model.UserGroup
+	model.DB.Where("group_id = ?", gid).Find(&userGroups)
+	var groupUsers []gin.H
+	for _, ug := range userGroups {
+		var u model.User
+		if err := model.DB.First(&u, ug.UserID).Error; err == nil {
+			groupUsers = append(groupUsers, gin.H{
+				"id": u.ID, "username": u.Username, "display_name": u.DisplayName, "role": u.Role,
+			})
+		}
+	}
+	if groupUsers == nil {
+		groupUsers = []gin.H{}
+	}
+
 	return gin.H{
 		"id":                      group.ID,
 		"name":                    group.Name,
@@ -309,6 +351,9 @@ func enrichGroup(group model.InstanceGroup) gin.H {
 		"user_count":              userCount,
 		"readonly_instance_ids":   collectInstanceIDs(readonlyMembers),
 		"write_instance_ids":      collectInstanceIDs(writeMembers),
+		"readonly_instances":      readonlyInstances,
+		"write_instances":         writeInstances,
+		"users":                   groupUsers,
 	}
 }