feat(gateway): 账号在线三态（后端 AccountStatus 可选接口 + 面板第二枚标签 + 契约账目更正）

- known=false ⇒ accountOnline 键**缺席**（未知 ≠ 离线），与既有 connected 语义并列不合并
- 面板：账号在线/账号离线/账号状态未知 三态 + 中性灰 tone + 「这不等于离线」悬停说明
- 测试：gateway 跨层锁「键缺席」（用真 qq_obv11.Adapter）+ 面板 61/40 断言
- 变异：known 当离线 ⇒ 两条测试同时红（已复跑确认）
- Docs/api-client.md：§7.2 那行由未实现改已实现（留表，注明下版移入 §7.1）

internal/services/gateway/admin_query.go

@@ -63,6 +63,7 @@ func (s *Server) adminListChannels(w http.ResponseWriter, r *http.Request) {
 	accountsByPlatform := s.maskedChannelAccounts()
 	botByPlatform := s.liveBotIdentity()
 	connectedByPlatform := s.liveAccountConnections()
+	onlineByPlatform := s.liveAccountOnline()
 	out := make([]ChannelSummary, 0)
 	if s.caps != nil {
 		for _, cap := range s.caps.List(capreg.KindChannel) {
@@ -98,7 +99,10 @@ func (s *Server) adminListChannels(w http.ResponseWriter, r *http.Request) {
 				}
 			}
 			if accts, ok := accountsByPlatform[platform]; ok && len(accts) > 0 {
-				sum.Accounts = enrichAccountsWithConnection(enrichAccountsWithBot(accts, botByPlatform[platform]), connectedByPlatform[platform])
+				sum.Accounts = enrichAccountsWithAccountOnline(
+					enrichAccountsWithConnection(enrichAccountsWithBot(accts, botByPlatform[platform]), connectedByPlatform[platform]),
+					onlineByPlatform[platform],
+				)
 			}
 			out = append(out, sum)
 		}