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.

.github/workflows/release.yml

@@ -28,7 +28,7 @@ jobs:
         run: |
           VERSION="${GITHUB_REF_NAME#v}"
           mkdir "awgcontrol-${VERSION}"
-          cp -r awg-ctrl awg-ui cli .env "awgcontrol-${VERSION}/"
+          cp -r awg-ctrl awg-ui awg-agent cli .env "awgcontrol-${VERSION}/"
           tar --exclude='node_modules' -czf "awgcontrol-${VERSION}.tar.gz" "awgcontrol-${VERSION}/"
 
       - name: Publish release