fix(puter): add protocol to config, fix(fleet): use Debian 12

Puter: protocol was missing from config.json, causing origin to be
computed as 'undefined://IP:4100'. All API/WebSocket URLs inherited
this broken value, making the frontend unable to load.

Fleet: MySQL APT repo requires Debian 12 (Bookworm), not 13.

ct/fleet.sh

@@ -11,7 +11,7 @@ var_cpu="${var_cpu:-2}"
 var_ram="${var_ram:-2048}"
 var_disk="${var_disk:-8}"
 var_os="${var_os:-debian}"
-var_version="${var_version:-13}"
+var_version="${var_version:-12}"
 var_unprivileged="${var_unprivileged:-1}"
 
 header_info "$APP"