feat(remote-builders): build ai and shoukei on aquamarine (#467)

Aquamarine builds for ai and shoukei across the three platforms, with both
daemons logging in as root. They authenticate with their passphrase-free SSH
host keys, and ssh_known_hosts now carries each builder's address.

Assisted-by: DeepSeek Harness 0.2.0-rc.2 (deepseek-flash)

hosts/12kingdoms-shoukei/default.nix

@@ -19,6 +19,10 @@ in
     ../idols-ai/preservation.nix
   ];
 
+  # 16G on a laptop: heavy derivations go to aquamarine's 96G instead of
+  # swapping here.
+  modules.remote-builders.enable = true;
+
   # disable sunshine for security
   services.sunshine.enable = lib.mkForce false;