fix(online): scope online status per node instead of a global union

The inbounds page and Nodes page checked each client's email against a
single deduped union of every node's online clients, so a client connected
to one node showed as online on every inbound across every node. The local
online set was also derived from the email-keyed client_traffics.last_online
column, which remote-node syncs bump too, leaking remote-only clients onto
local inbounds.

Track online clients per node: the local panel's own xray clients under key
0 (derived from live traffic-poll deltas via RefreshLocalOnline, kept in
memory and independent of the shared last_online column) and each remote
node under its id. Add GetOnlineClientsByNode plus a /clients/onlinesByNode
endpoint and onlineByNode WS field; node.go and the inbounds rollup now scope
online by node. The flat GetOnlineClients union is kept for client-centric and
total-count views (Clients page, dashboard, telegram).

Closes #4809

web/controller/client.go

@@ -55,6 +55,7 @@ func (a *ClientController) initRouter(g *gin.RouterGroup) {
 	g.POST("/ips/:email", a.getIps)
 	g.POST("/clearIps/:email", a.clearIps)
 	g.POST("/onlines", a.onlines)
+	g.POST("/onlinesByNode", a.onlinesByNode)
 	g.POST("/lastOnline", a.lastOnline)
 }
 
@@ -397,6 +398,10 @@ func (a *ClientController) onlines(c *gin.Context) {
 	jsonObj(c, a.inboundService.GetOnlineClients(), nil)
 }
 
+func (a *ClientController) onlinesByNode(c *gin.Context) {
+	jsonObj(c, a.inboundService.GetOnlineClientsByNode(), nil)
+}
+
 func (a *ClientController) lastOnline(c *gin.Context) {
 	data, err := a.inboundService.GetClientsLastOnline()
 	jsonObj(c, data, err)