chore(nix): update flake.lock with playwright-web-flake

Update all flake inputs:
- Added playwright-web-flake input (pinned to 1.56.1)
- Updated nixpkgs (2025-10-02 → 2025-10-28)
- Updated flake-parts (2025-10-01 → 2025-10-20)
- Updated git-hooks (2025-10-03 → 2025-10-17)

The playwright-web-flake input provides version-locked browsers that
exactly match the @playwright/test version in package.json.

Author: cameronraysmith