feat: 用户订阅显示节点分组名及限速起止时间

- UserSubscribe/UserSubscribeDetail 新增 node_group_id/node_group_name 字段
- 管理员查询用户订阅列表批量填充分组名
- 管理员查询单个订阅详情填充分组名
- ThrottleResult/UserSubscribeDetail 新增 throttle_start/throttle_end 字段
- 限速时返回限速窗口起止时间（秒级 Unix 时间戳）

Co-Authored-By: claude-flow <ruv@ruv.net>

pkg/speedlimit/calculator.go

@@ -19,11 +19,13 @@ type TrafficLimitRule struct {
 
 // ThrottleResult contains the computed speed limit status for a user subscription.
 type ThrottleResult struct {
-	BaseSpeed     int64   `json:"base_speed"`      // Plan base speed limit (Mbps, 0=unlimited)
-	EffectiveSpeed int64  `json:"effective_speed"`  // Current effective speed limit (Mbps)
-	IsThrottled   bool    `json:"is_throttled"`     // Whether the user is currently throttled
-	ThrottleRule  string  `json:"throttle_rule"`    // Description of the matched rule (empty if not throttled)
-	UsedTrafficGB float64 `json:"used_traffic_gb"`  // Traffic used in the matched rule's window (GB)
+	BaseSpeed      int64   `json:"base_speed"`       // Plan base speed limit (Mbps, 0=unlimited)
+	EffectiveSpeed int64   `json:"effective_speed"`  // Current effective speed limit (Mbps)
+	IsThrottled    bool    `json:"is_throttled"`     // Whether the user is currently throttled
+	ThrottleRule   string  `json:"throttle_rule"`    // Description of the matched rule (empty if not throttled)
+	UsedTrafficGB  float64 `json:"used_traffic_gb"`  // Traffic used in the matched rule's window (GB)
+	ThrottleStart  int64   `json:"throttle_start"`   // Window start Unix timestamp (seconds), 0 if not throttled
+	ThrottleEnd    int64   `json:"throttle_end"`     // Window end Unix timestamp (seconds), 0 if not throttled
 }
 
 // Calculate computes the effective speed limit for a user subscription,
@@ -89,6 +91,8 @@ func Calculate(ctx context.Context, db *gorm.DB, userId, subscribeId, baseSpeedL
 					result.EffectiveSpeed = rule.SpeedLimit
 					result.IsThrottled = true
 					result.UsedTrafficGB = usedGB
+					result.ThrottleStart = startTime.Unix()
+					result.ThrottleEnd = now.Unix()
 
 					statLabel := "小时"
 					if rule.StatType == "day" {