Prometheus on a node; panel under a URL prefix; open ports on migrate import

A panel without VPN (e.g. after the move) can use a Prometheus that lives on
a node, such as the one with history left on the old server (node #0). Both
directions go through the agent's WSS: the node's Prometheus scrapes
127.0.0.1:AGENT_METRICS_PORT/metrics, the agent checks its token and asks
core (metrics → metrics_res, the same exposition as /metrics, at most once
per 5 s per connection); the monitor tab reads it back through the agent,
which forwards only GET /-/ready and /api/v1/query[_range]. The panel finds
it by itself (local first, then the lowest-id node), and the install/remove
buttons work on a panel without VPN. `monitor install` on a node without its
own panel picks AGENT_METRICS_PORT, writes it to cli.env and restarts the
agent; on the old server it keeps the collected data.

The panel works behind nginx in a subfolder: relative asset and API paths,
relative directory redirects, and the client address from X-Forwarded-For /
X-Real-IP only from trusted proxies (loopback, TRUST_PROXY).

migrate import opens the moved SUB_PORT/NODE_PORT in UFW when it is active.

internal/ui/web.go

@@ -212,12 +212,13 @@ func (c *Ctx) Obj() jsjson.Object {
 }
 
 // remoteIP — req.socket.remoteAddress.
+// remoteIP — адрес клиента; за доверенным reverse-proxy — из его заголовков (trustproxy.go).
 func (c *Ctx) remoteIP() string {
 	host, _, err := net.SplitHostPort(c.R.RemoteAddr)
 	if err != nil {
 		return "unknown"
 	}
-	return host
+	return clientIP(host, c.R.Header, trustedProxies())
 }
 
 // hostname — req.hostname в Express (trust proxy выключен): Host без порта, у IPv6 — в скобках.