fix: remaining DHCP drifts + improve validation script

- Fixed apps LXC 105: /etc/network/interfaces was still 'iface eth0 inet
  dhcp' -> changed to static 192.168.8.205/24, killed dhclient, applied
- Fixed mule-images LXC 120: DHCP client had overridden static .136 with
  DHCP lease .108 -> killed dhclient, restored .136
- Fixed sophia docs: inventory said .157, actual Proxmox config is .109
- Updated check-caddy-backends.sh: uses curl with connect-timeout for
  reliable TCP checks, distinguishes 'port open / no HTTP' from 'unreachable'

inventory.yaml

@@ -221,7 +221,7 @@ hosts:
     host: hubris
     os: linux
     role: workshop
-    lan_ip: 192.168.8.157
+    lan_ip: 192.168.8.109
     mesh:
       tailscale:
         fqdn: sophia