feat(theme): unified typography config + defineTheme API cleanup

[cixzhang]

Implements #802 — restructures defineTheme to unify font, scale, and weight config under a single typography object, and renames motionScale/radiusScale to motion/radius.

API Changes

Before	After
typeScale: { base, ratio }	typography: { scale: { base, ratio } }
typeScale.weights.heading	typography.heading: { weight, weights }
fonts: [{ family, url }]	typography.body: { family, fallbacks, url }
tokens: { '--font-body': '...' }	typography.body: { family, fallbacks }
motionScale: { fast, medium, ratio }	motion: { fast, medium, ratio }
radiusScale: { base, multiplier }	radius: { base, multiplier }

Typography roles

• body, heading, code — each declares family, fallbacks, url, weight
• heading inherits family/fallbacks/url from body if omitted
• FontWeight type: 'normal' | 'medium' | 'semibold' | 'bold' (raw CSS values as escape hatch)
• defineTheme derives --font-body/heading/code tokens and fonts[] for runtime loading

Theme updates

Default — minimal change:

typography: { scale: { base: 14, ratio: 1.2 } },
motion: { fast: 175, medium: 410, ratio: 0.75 },

Neutral — fonts move from token overrides into typography roles:

typography: {
  scale: { base: 14, ratio: 1.2 },
  body: { family: 'Geist', fallbacks: '"Geist Fallback", -apple-system, ...' },
  heading: { weights: { 3: 'bold', 4: 'bold' } },
  code: { family: 'Geist Mono', fallbacks: '"SF Mono", Monaco, ...' },
},

Brutalist — typography.body sets Courier for everything (heading inherits), eliminates both the --font-heading token override and the text.base.fontFamily component override:

typography: {
  body: { family: 'Courier New', fallbacks: '"Courier", monospace' },
},

Test coverage

• 55 defineTheme tests (was 45) — new tests for font derivation, weight mapping, heading inheritance
• 15 generateThemeRules tests — updated to new API
• All 1827 tests pass

Closes #802.

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[github-actions]

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No new or modified components detected.

Bundle Size Summary

Package	Size (ESM)	Size (CJS)	Gzipped
@xds/core	11.0KB	17.5KB	2.7KB

Accessibility Audit

Status: No accessibility violations detected.

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