Storybook CI on GitHub Actions

Building a static Storybook takes as long as the app itself.

Why it happens

The Storybook build has no persistent cache and often rebuilds every story from scratch.

What to change

1. Cache node_modules/.cache/storybook keyed on the lockfile
2. Build Storybook only when stories or components changed, using path filters
3. Run visual regression tests against the built output rather than rebuilding per test

Storybook on runnerhut

jobs:
  storybook:
    runs-on: runnerhut-4vcpu-ubuntu-2404
    steps:
      - uses: actions/checkout@v4
      - run: npm ci
      - run: npx storybook build

The only runnerhut-specific line is `runs-on: runnerhut-4vcpu-ubuntu-2404`. Everything else is standard GitHub Actions — the same actions, the same secrets and the same permissions model you use today.