Switches the nix branch prefix from release to nixos. release-YY.MM are
the development branches, while nixos-YY.MM are the intended ones for
use.
Targeting release risks pinning untested code and often leads to
rebuilding big packages when the nix cache has not caught up.
Flake lock file updates:
• Updated input 'nixpkgs':
'github:NixOS/nixpkgs/8cb14136bb517eba32a565a682861eef55c45a06'
(2026-06-29)
→ 'github:NixOS/nixpkgs/4382ed2b7a6839d4280a9b386db49cbc5907414d'
(2026-07-16)
Provide non-flake solution by pinning in shell.nix
Invoking `nix-shell` makes shell.nix not consume the flake. Importing
`<nixpkgs>` is dependent on the user's current nixpkgs channel. This is not
reproducible.
Fix this by pinning nixpkgs to the same revision of the flake input.
