Sync host lists with flake.nix and add CLAUDE.md

Remove the nonexistent kuma host and add the missing linode-minimal
host across README, AGENTS.md, docs, and CI eval workflows so they
match flake.nix's nixosConfigurations. Also add CLAUDE.md with
architecture/safety guidance for future Claude Code sessions.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

.github/workflows/check-nixos.yml

@@ -20,7 +20,7 @@ jobs:
       - name: Evaluate all NixOS hosts
         run: |
           set -euo pipefail
-          for host in nixos docker kuma server nix-cache nix-minimal pxe-boot; do
+          for host in nixos docker server nix-cache nix-minimal pxe-boot linode-minimal; do
             echo "Evaluating ${host}"
             nix --extra-experimental-features 'nix-command flakes' eval \
               ".#nixosConfigurations.${host}.config.system.build.toplevel.drvPath" --raw