feat(design-system): improve code quality in Storybook files [AR-74627]

[iromanchuk-dn]

Improved components

Component	Stories	Docs snapshot	New browser test	Cleanup (SCSS/impl)
ds-alert-banner	✓	✓
ds-autocomplete	✓	✓
ds-avatar		✓
ds-avatar-group	✓	✓	✓	✓ (scss, tsx, types)
ds-card	✓	✓	✓	✓ (scss, tsx)
ds-catalog-layout	✓	✓
ds-checkbox	✓	✓		✓ (scss, tsx)
ds-date-picker	✓	✓		✓ (scss, tsx, types)
ds-date-range-picker	✓	✓		✓ (scss)
ds-dialog	✓	✓	✓	✓ (scss, tsx)

Notes:

• All 10 had their *.stories.tsx cleaned up for code quality and were opted into the docs-snippet tests (each got a colocated *.docs.snap golden file).
• ds-avatar only shows a snapshot file because its stories were already clean — just newly covered by the docs tests.
• Three (ds-avatar-group, ds-card, ds-dialog) also gained new *.browser.test.tsx coverage.
• ds-date-range-picker is the one whose snapshot I regenerated in the CI fix (timezone determinism).

For reference, ds-breadcrumb and ds-button-v3 are also in the docs-test allowlist but were the reference components set up in the earlier docs-tests PR (#587), not part of this branch's component improvements.

[netlify]

✅ Deploy Preview for drivenets-design-system ready!

Name	Link
🔨 Latest commit	4480171
🔍 Latest deploy log	https://app.netlify.com/projects/drivenets-design-system/deploys/6a60af03dd9f0a0008a12f89
😎 Deploy Preview	https://deploy-preview-614--drivenets-design-system.netlify.app
📱 Preview on mobile	Toggle QR Code... Use your smartphone camera to open QR code link.
🤖 Make changes	Run an agent on this branch

---

To edit notification comments on pull requests, go to your Netlify project configuration.