flake.lock: Update

Flake lock file updates:

• Updated input 'emacs-overlay':
    'github:nix-community/emacs-overlay/568d473' (2026-01-24)
  → 'github:nix-community/emacs-overlay/91add9b' (2026-01-31)
• Updated input 'home-manager':
    'github:nix-community/home-manager/2539eba' (2026-01-24)
  → 'github:nix-community/home-manager/f4ad506' (2026-01-31)
• Updated input 'nixpkgs':
    'github:nixos/nixpkgs/88d3861' (2026-01-21)
  → 'github:nixos/nixpkgs/bfc1b8a' (2026-01-26)

Author: github-actions[bot]