chore(deps): update flake.lock

Flake lock file updates:

• Updated input 'nixpkgs':
    'github:nixos/nixpkgs/f560cce' (2025-12-26)
  → 'github:nixos/nixpkgs/30a3c51' (2026-01-03)
• Updated input 'nixpkgs-unstable':
    'github:nixos/nixpkgs/c0b0e0f' (2025-12-28)
  → 'github:nixos/nixpkgs/fb7944c' (2026-01-02)
• Updated input 'system-manager':
    'github:numtide/system-manager/bd3e419' (2025-12-17)
  → 'github:numtide/system-manager/4434112' (2025-12-30)
• Updated input 'treefmt-nix':
    'github:numtide/treefmt-nix/42d96e7' (2025-12-17)
  → 'github:numtide/treefmt-nix/d56486e' (2026-01-03)

Author: github-actions[bot]