fix(nix): commit a consistent flake.lock so builds don't rewrite it

The release `nix-cache` job built and pushed to the public cache, then
`kup publish` aborted with:

    warning: Git tree '…/komet-node' is dirty
    ❗ Repository is dirty, aborting!

Root cause: the flake.lock committed in #16 was hand-edited and inconsistent
with flake.nix. On a clean checkout, the first `nix build` reconciles it
("updating lock file …"), which dirties the working tree; `kup publish`
refuses to publish from a dirty repo.

Regenerate flake.lock with `nix flake lock` so it is internally consistent:
normalize the pyproject-build-systems / pyproject-nix `follows` paths and add
the previously-missing `rv-nix-tools/nixpkgs` node. The resolved revisions are
unchanged — uv2nix stays 9d357f0 and pyproject-nix stays d6c61db (the fixed
pep600 revision) — so this is pure lock bookkeeping with no input bumps.

Validated on a pristine worktree of main: with this lock committed,
`nix build .#komet-node` performs no lock update and leaves the tree clean
(`git status` empty), which is exactly the condition `kup publish` gates on.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

Author: RaoulSchaffranek