- Add the agent profile (modules/nixos/agent.nix: rootless Podman, linger,
nix-ld) with home/linux/tui.nix as its home role; ruby, kana and
aquamarine use it, so hosts no longer import from hosts/idols-ruby.
- Gate nushell's ~/.secrets source behind modules.shell.secrets.enable,
off on agent hosts.
- Persist the TUI home state on aquamarine's tmpfs root.
- Document host profiles in hosts/README.md; add tests/agent-profile and
drop the x86_64 colmena-parity test, which needs mysecrets.
Assisted-by: Claude Code (claude-opus-5-5)