Closes #1.

The package was pinned at ^1.5.0 while the rest of the family moved
to 2.x. Consumers running with strict-peer-dependencies (pnpm,
modern npm) couldn't install fancy-code alongside react-fancy ≥ 2.
Aligned with fancy-sheets which already declares ^2.0.0.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>