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.

awg-ui/src/main.tsx

@@ -3,8 +3,17 @@
 // LICENSE file in the root directory of this source tree.
 import { StrictMode } from 'react';
 import { createRoot } from 'react-dom/client';
+import axios from 'axios';
 import App from './App';
 
+// Пути к API в коде пишутся от корня («/ui/nodes»), а уходят от адреса страницы («ui/nodes»):
+// так панель за reverse-proxy в подпапке (example.com/forgetting/) ходит в свой префикс, а в корне
+// всё как раньше. Одно место на все запросы, включая будущие.
+axios.interceptors.request.use(c => {
+    if (c.url?.startsWith('/') && !c.url.startsWith('//')) c.url = c.url.slice(1);
+    return c;
+});
+
 createRoot(document.getElementById('root')!).render(
     <StrictMode>
         <App />