flake.lock: Update

Flake lock file updates:

• Updated input 'home-manager':
    'github:nix-community/home-manager/f894bc4' (2026-01-04)
  → 'github:nix-community/home-manager/4e8b7be' (2026-01-06)
• Updated input 'nix-darwin':
    'github:nix-darwin/nix-darwin/c31afa6' (2025-12-29)
  → 'github:nix-darwin/nix-darwin/9f48ffa' (2026-01-06)
• Updated input 'nixpkgs':
    'github:nixos/nixpkgs/fb7944c' (2026-01-02)
  → 'github:nixos/nixpkgs/9f0c42f' (2026-01-05)

Author: github-actions[bot]