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/vite.config.ts

@@ -5,6 +5,10 @@ import { defineConfig } from 'vite';
 import react from '@vitejs/plugin-react';
 
 export default defineConfig({
+    // Ресурсы — от адреса страницы, а не от корня домена: собранная панель работает и в корне, и в
+    // подпапке за reverse-proxy (example.com/forgetting/) без пересборки. Запросы к API — так же
+    // (main.tsx).
+    base: './',
     plugins: [react()],
     server: {
         proxy: {