- Bump the nixpkgs input and allow unfree packages.
- Add claude-code to the devShell.
- Switch from nodejs_22 to nodejs_24 to match CI (tests:unit's
--test-isolation flag needs a Node version where it's no longer
experimental).
- Add cairo/pango/libjpeg/giflib/librsvg/pixman/util-linux as build and
runtime deps, plus pkg-config/python3/gnumake, so the canvas npm
package (used by an impro unit test) can be rebuilt from source instead
of relying on its prebuilt binary, which isn't ABI-compatible with
nixpkgs' cairo/freetype.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>