Address PR review feedback: in-file comments should describe only what the
file currently is, not task numbers, external tooling, or past/future states.
- hosts/neogaia: drop the "replaced by disko in task 0002" / "arrive in later
tasks" framing; describe the filesystems and hardware profile as the
placeholder values they are.
- lib: drop the "no null-placeholder traversal hack" comparison to a prior
implementation.
- system: drop "no impure environment lookup" from the user.name description
and the sops/post-boot roadmap from the user comment.