feat(subscribe): add traffic limit rules and user traffic stats

- Add subscribe traffic_limit schema and migration\n- Support traffic_limit in admin create/update and list/details\n- Apply traffic_limit when building server user list speed limits\n- Add public user traffic stats API

apis/public/user.api

@@ -144,6 +144,22 @@ type (
 		HistoryContinuousDays   int64 `json:"history_continuous_days"`
 		LongestSingleConnection int64 `json:"longest_single_connection"`
 	}
+	GetUserTrafficStatsRequest {
+		UserSubscribeId string `form:"user_subscribe_id" validate:"required"`
+		Days            int    `form:"days" validate:"required,oneof=7 30"`
+	}
+	DailyTrafficStats {
+		Date     string `json:"date"`
+		Upload   int64  `json:"upload"`
+		Download int64  `json:"download"`
+		Total    int64  `json:"total"`
+	}
+	GetUserTrafficStatsResponse {
+		List          []DailyTrafficStats `json:"list"`
+		TotalUpload   int64               `json:"total_upload"`
+		TotalDownload int64               `json:"total_download"`
+		TotalTraffic  int64               `json:"total_traffic"`
+	}
 )
 
 @server (
@@ -271,6 +287,10 @@ service ppanel {
 	@doc "Delete Current User Account"
 	@handler DeleteCurrentUserAccount
 	delete /current_user_account
+
+	@doc "Get User Traffic Statistics"
+	@handler GetUserTrafficStats
+	get /traffic_stats (GetUserTrafficStatsRequest) returns (GetUserTrafficStatsResponse)
 }
 
 @server (