v0.3.1 - Storybook docs infrastructure + first 5 components

Pre-release. Not for production use.

Storybook documentation

• 2-tab pattern established: Guidance (MDX) + Playground per component
• 5 components documented: Button, Link, Icon Button, Breadcrumb, Intro Text
• Shared icon helper with categorized HDS/USWDS icon arrays
• Palette switcher toolbar for testing all 6 palettes
• Note callout system (USWDS/Figma/Code variants)

CSS fixes

• Breadcrumb: slash separators, palette-aware colors, hover states
• Intro Text: corrected to match Figma spec (size, weight, line-height, letter-spacing)
• Icon Button interactive role: hardcoded colors instead of palette vars
• Breadcrumb separator: forward slash override (from nasa.gov production pattern)

Infrastructure

• Prettier configured (proseWrap: never)
• Storybook: dynamic source, disabled save-from-UI
• Component roadmap published as GitHub Discussion

What's next

See #8 (and add comments on any components you need for your site!)