feat: 限速状态可视化 - 后台订阅详情展示实际限速与降速状态

- 新增 pkg/speedlimit/calculator.go 公共限速计算函数
- UserSubscribeDetail 响应新增 effective_speed/is_throttled/throttle_rule 字段
- GetUserSubscribeById 接口查询时实时计算并返回限速状态
- 重构 getServerUserListLogic 的 calculateEffectiveSpeedLimit，改用共享函数

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

internal/types/types.go

@@ -3278,24 +3278,27 @@ type UserSubscribe struct {
 }
 
 type UserSubscribeDetail struct {
-	Id          int64     `json:"id"`
-	UserId      int64     `json:"user_id"`
-	User        User      `json:"user"`
-	OrderId     int64     `json:"order_id"`
-	SubscribeId int64     `json:"subscribe_id"`
-	Subscribe   Subscribe `json:"subscribe"`
-	NodeGroupId int64     `json:"node_group_id"`
-	GroupLocked bool      `json:"group_locked"`
-	StartTime   int64     `json:"start_time"`
-	ExpireTime  int64     `json:"expire_time"`
-	ResetTime   int64     `json:"reset_time"`
-	Traffic     int64     `json:"traffic"`
-	Download    int64     `json:"download"`
-	Upload      int64     `json:"upload"`
-	Token       string    `json:"token"`
-	Status      uint8     `json:"status"`
-	CreatedAt   int64     `json:"created_at"`
-	UpdatedAt   int64     `json:"updated_at"`
+	Id             int64     `json:"id"`
+	UserId         int64     `json:"user_id"`
+	User           User      `json:"user"`
+	OrderId        int64     `json:"order_id"`
+	SubscribeId    int64     `json:"subscribe_id"`
+	Subscribe      Subscribe `json:"subscribe"`
+	NodeGroupId    int64     `json:"node_group_id"`
+	GroupLocked    bool      `json:"group_locked"`
+	StartTime      int64     `json:"start_time"`
+	ExpireTime     int64     `json:"expire_time"`
+	ResetTime      int64     `json:"reset_time"`
+	Traffic        int64     `json:"traffic"`
+	Download       int64     `json:"download"`
+	Upload         int64     `json:"upload"`
+	Token          string    `json:"token"`
+	Status         uint8     `json:"status"`
+	EffectiveSpeed int64     `json:"effective_speed"`
+	IsThrottled    bool      `json:"is_throttled"`
+	ThrottleRule   string    `json:"throttle_rule,omitempty"`
+	CreatedAt      int64     `json:"created_at"`
+	UpdatedAt      int64     `json:"updated_at"`
 }
 
 type UserSubscribeInfo struct {