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.

install/puter-install.sh

@@ -41,6 +41,7 @@ cat <<EOF >/etc/puter/config.json
 {
   "config_name": "proxmox",
   "domain": "${LOCAL_IP}",
+  "protocol": "http",
   "http_port": 4100,
   "experimental_no_subdomain": true,
   "services": {