feat(nixos): migrate system configuration

README.md

@@ -6,6 +6,8 @@ This is my monorepo, started in 2026.
 ```
 dev/                Monorepo root
 ├── .archive/       Archived projects
+├── configs/        Declarative configuration
+│   └── nixos/      NixOS hosts, modules, guests, registry, and secrets
 ├── docs/           Obsidian vault / Second brain
 ├── src/            Projects
 │   └── tools/      Projects that are tools