feat: /export-design-system command for publishable component libraries

[PAMulligan]

Summary

• Adds a standalone /export-design-system slash command, an export-design-system skill, and a scripts/export-design-system.{js,sh} exporter that emits a publishable pnpm workspace from generated components and design-tokens.lock.json.
• Output: @scope/design-tokens (framework-agnostic — CSS vars, Tailwind preset, typed exports) plus @scope/<framework>-components (built with Vite library mode for React/Vue/Svelte; tsc for React Native, since Vite is incompatible with the RN runtime).
• Scoped to whatever outputTarget is set in build-spec.json (with --framework flag and package.json-based fallback). Includes Changesets versioning scaffold, .npmrc, per-package READMEs, and a ThemeProvider + useTheme per framework.

Closes #19.

What's in the box

• scripts/export-design-system.js — main exporter (~640 LOC, ESM, no extra deps)
• scripts/export-design-system.sh — wrapper matching the generate-stories.sh pattern
• .claude/commands/export-design-system.md — slash command
• .claude/skills/export-design-system/SKILL.md — skill docs
• CLAUDE.md — registered new script + skill + command, count bumps (19→20 skills, 29→31 scripts)

Test plan

• --help renders correctly
• React: auto-detects outputTarget from build-spec.json, scope from package.json, copies components + index.ts, excludes *.test.* / *.stories.* / *.d.ts
• Vue: .vue components copied, ThemeProvider.ts uses provide/inject + h() render
• Svelte: .svelte components, ThemeProvider.svelte, vite-plugin-svelte config
• React Native: no vite.config.ts, tsc -p tsconfig.json build, peerDeps react-native >=0.74, RN note in stdout + README
• Existing output dir: refuses without --force (exit 1), overwrites with --force
• Missing inputs: clear error, exit 2
• Unsupported framework (--framework angular): exit 3
• --dry-run: writes nothing
• --json: machine-readable summary
• Cross-platform tokens-package build: cp replaced with a generated scripts/postbuild.mjs using fs.cpSync (caught during smoke testing on Windows)
• End-to-end: pnpm install && pnpm build against a real lockfile from a /build-from-figma run (not yet exercised — peer-dep ranges and Tailwind preset mapping may need tweaks for non-standard lockfile shapes)

Caveats

• The script writes files only — it does not run pnpm install or pnpm build. First real proof-of-life will come from running the workspace against a real lockfile.
• Tailwind preset assumes lockfile keys colors, spacing, radii/borderRadius, typography.fontFamily. Non-standard shapes may require a hand-tweak to the generated preset.
• React Native uses tsc not Vite. Documented in stdout, README, and skill docs.

🤖 Generated with Claude Code