fix(remote): correct hbbs relay flag to lowercase -r

The previous commit used `hbbs -R 192.168.1.69` (uppercase -R sets
rendezvous/cluster servers), so hbbs advertised an empty relay list and
clients failed with "failed to connect to relay server". Lowercase -r is
the relay-server flag; hbbs now advertises 192.168.1.69 and LAN clients
relay correctly.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

stacks/remote/docker-compose.yml

@@ -18,7 +18,7 @@ services:
   hbbs:
     container_name: hbbs
     image: rustdesk/rustdesk-server:latest
-    command: hbbs -R 192.168.1.69
+    command: hbbs -r 192.168.1.69
     restart: unless-stopped
     env_file:
       - stack.env