[Theme typography/contracts] Investigate and add serializable typography scale contracts

[artiphishle]

Summary

Investigate common typography scale models and add serializable typography scale contracts to @ankhorage/contracts.

Typography should be treated as a sibling system to spacing. It should not be folded into the spacing issue because typography has additional concerns: type scale model, font family, line height, font weight, letter spacing, responsive/fluid behavior, accessibility scaling, locale/script support, and semantic text roles.

Architecture

• @ankhorage/contracts owns serializable typography scale config and preset names.
• @ankhorage/zora owns semantic text recipes and component interpretation.
• @ankhorage/surface owns low-level rendered text primitives.
• ankhorage4 / Studio can later expose typography preset and density controls in the theme creator.

Research scope

Investigate at least these models/presets:

• Ankhorage default curated product-app scale
• Material 3 type roles
• Tailwind font-size scale
• Carbon productive and expressive type sets
• Atlassian typography scale
• GOV.UK fixed/responsive type scale
• modular type scale
• fluid/responsive type scale, e.g. Utopia-like model
• custom scale

Contract scope

Add serializable types such as:

• ThemeTypographyPreset
• ThemeTypographyDensity
• ThemeTypographyScaleModel
• ThemeTypographyScaleConfig
• custom typography token shape

The contract should support fixed, modular, and later fluid models without requiring runtime functions in manifests.

Suggested shape

export type ThemeTypographyPreset =
  | 'ankhorage'
  | 'material3'
  | 'tailwind'
  | 'carbon-productive'
  | 'carbon-expressive'
  | 'atlassian'
  | 'govuk'
  | 'modular'
  | 'fluid'
  | 'custom';

export type ThemeTypographyDensity = 'compact' | 'default' | 'comfortable';

export type ThemeTypographyScaleModel = 'fixed' | 'modular' | 'fluid';

export interface ThemeTypographyTokenConfig {
  fontSize: number;
  lineHeight: number;
  letterSpacing?: number;
  fontWeight?: number | string;
}

export interface ThemeTypographyScaleConfig {
  preset: ThemeTypographyPreset;
  model?: ThemeTypographyScaleModel;
  density?: ThemeTypographyDensity;
  baseSize?: number;
  ratio?: number;
  minViewport?: number;
  maxViewport?: number;
  minBaseSize?: number;
  maxBaseSize?: number;
  minRatio?: number;
  maxRatio?: number;
  tokens?: Record<string, ThemeTypographyTokenConfig>;
}

Final names may differ if implementation finds a cleaner contract shape.

Acceptance criteria

• @ankhorage/contracts exposes serializable typography scale config types.
• ThemeConfig can carry typography scale selection without importing ZORA or Surface.
• Supported typography presets/models are explicit and documented.
• Fixed, modular, fluid, and custom models are representable as data.
• Tests cover representative preset, modular, fluid, and custom configs.
• README/docs explain the boundary between contracts and ZORA recipes.
• bun run build, bun run lint:fix, and bun run test pass.

Non-goals

• Do not implement ZORA Text or Heading recipes in this repo.
• Do not migrate ZORA components in this issue.
• Do not add non-serializable functions or callbacks.
• Do not implement Studio UI in this issue.