feat: switch to incus-lts and fix lab-tool SSH syntax

- Use incus-lts (6.0.4) instead of latest incus to avoid cowsql build issues
- Re-enable incus on congenital-optimist with LTS version
- Restore incus-admin group membership for users
- Fix missing parentheses in lab-tool SSH module
- This provides stable containerization without build failures

modules/users/sma.nix

@@ -21,6 +21,7 @@
       "wheel" # sudo access
       "networkmanager" # network management
       "libvirt" # virtualization management
+      "incus-admin" # container management
       "podman" # container runtime
       "docker" # docker compatibility (if needed)
       "media" # shared media access for NFS shares