Fix flake apps schema for nixinate compatibility with flake check

[wiesesamuel]

Hi Matthew,
when i followed the README guide an inserted the apps declaration nix flake check failed.
However i got it working using the following fix.
Thanks for your work!
Best Greetings,
Samuel

Summary:
nix flake check failed with

error: 'nixinate' is not a valid system type

because the generated apps attribute wasn’t nested under the system key (apps.x86_64-linux).

Fix:
Scope the nixinate apps correctly under the system:

# before
apps = nixinate.nixinate.${system} self;

# after
apps.${system} = (nixinate.nixinate.${system} self).nixinate;

This makes nix flake check succeed and exposes apps as
apps.x86_64-linux.myMachine.

Result:
✅ nix flake show works
✅ nix flake check passes
✅ nix run .#myMachine still works as expected