Cut restated "what", domain-glossary framing, cross-file consumption
narration, and against-alternative justification from in-file comments;
keep only non-obvious "why" and load-bearing pointers. Drop the
`generateCompletions` line (a no-op restatement of the upstream default)
and its comment.
Add disko as a flake input (following nixpkgs) and wire its NixOS module
into the host-builder, so any Host can declare a disk layout while the
layout itself stays a per-Host concern.
neogaia's layout (hosts/neogaia/disk.nix): one GPT NVMe disk with a
systemd-boot EFI system partition and a LUKS container holding btrfs with
@root/@home/@nix subvolumes. The initrd prompts for the passphrase on a
normal boot. Swap is RAM-backed zram, so there is no on-disk swap
partition; zramSwap is enabled directly for now. The placeholder
fileSystems are removed since disko now derives them.
