## Motivation
The MLX version and git revision in nix/mlx.nix were hardcoded and had
to be manually kept in sync with uv.lock
## Changes
- flake.nix: Extract MLX git rev from uv.lock's source.git URL and pass
as uvLockMlxRev
- nix/mlx.nix: Use uvLockMlxVersion and uvLockMlxRev instead of
hardcoded values; remove version mismatch assertion
## Why It Works
uv.lock is already the source of truth — now Nix reads both version and
rev from it directly. The pinned fetchFromGitHub hash still guards
against unexpected changes.
ciaranbor
f28b2fd037