Manage several servers from one panel: core + nodes

A node is a VPN server without a panel. awg-agent on it dials the panel
(core) over an outbound WSS connection and runs the panel's requests on its
own awg-ctrl, which stays on 127.0.0.1 and is unchanged. No inbound port on
the node, works behind NAT.

- awg-ui/nodes.ts: node registry in ui.db, WSS hub on NODE_PORT with a
  self-signed cert whose SPKI pin goes into the join string, RPC with
  timeouts, health polling, /ui/nodes routes.
- Nodes enroll with a one-time awgjoin:// string (secret stored hashed,
  1 hour) and then authenticate by their own Ed25519 key. The agent checks
  the pin before sending anything and only forwards /health, /api/*, /awg/*.
- server_id 0 is the panel's own awg-ctrl; LOCAL_NODE=off makes the panel
  run without a VPN of its own. The panel picks a server with X-Server-Id,
  API keys use their server_id. sen:// still serves one server.
- UI: a card per server in the server bar, switching remounts the tab,
  «Добавить сервер» gives the join command.
- CLI: agent service, roles from cli.env, join / unjoin commands.
- Release archives include awg-agent.

awg-ui/src/tabs/apikeys/index.tsx

@@ -2,7 +2,7 @@
 // This source code is licensed under the MIT license found in the
 // LICENSE file in the root directory of this source tree.
 import { useState, useEffect, useCallback } from 'react';
-import { apiFetch, copyText, timeAgo, type ApiKey, type PageProps } from '../../lib/shared';
+import { apiFetch, copyText, timeAgo, getServerId, type ApiKey, type PageProps } from '../../lib/shared';
 import { IcoPlus, IcoTrash, IcoCopy } from '../../components/icons';
 import './apikeys.css';
 
@@ -26,7 +26,7 @@ export default function ApiKeysPage({ token, showMsg }: PageProps) {
 
     const createKey = useCallback(async () => {
         if (!label.trim()) return;
-        const r = await apiFetch('POST', '/ui/apikeys', token, { label: label.trim(), server_id: 0 });
+        const r = await apiFetch('POST', '/ui/apikeys', token, { label: label.trim(), server_id: getServerId() ?? 0 });
         if (r.error) { showMsg(r.error); return; }
         setLabel('');
         setCreated({ label: r.label, key: r.key });