chore(flake): update inputs

Flake lock file updates:

• Updated input 'llm-agents':
    'github:numtide/llm-agents.nix/b5a2e39' (2026-05-01)
  → 'github:numtide/llm-agents.nix/2ad1248' (2026-05-07)
• Updated input 'llm-agents/flake-parts':
    'github:hercules-ci/flake-parts/3107b77' (2026-04-01)
  → 'github:hercules-ci/flake-parts/0678d89' (2026-05-05)
• Updated input 'llm-agents/nixpkgs':
    'github:NixOS/nixpkgs/7aaa00e' (2026-04-30)
  → 'github:NixOS/nixpkgs/68a8af9' (2026-05-07)

Author: github-actions[bot]