fix: add semver 7.x to fix storybook build in CI

Storybook 10 imports semver/functions/sort.js which only exists in
semver 7.x. The root-level semver was 6.x (needed by babel), causing
ESM resolution in Node 20.x to fail in CI.

Adding semver ^7.x as a direct dependency forces the root-level
version to 7.x, which is backwards compatible with 6.x consumers.

Author: ThomasK33