Tailwind CSS v4 JSX export (#54)
* Add Tailwind CSS v4 JSX export format
- Add JSXFormat type ('openpencil' | 'tailwind') to sceneNodeToJSX/selectionToJSX
- Tailwind resolver (tailwind.ts): px→spacing (v4 multiplier), hex→color class,
fontSize/fontWeight/borderRadius named lookups with arbitrary value fallback
- Export: FRAME→div, TEXT→p, SECTION→section, className with TW utility classes
- CLI: export --format jsx --style tailwind
- CodePanel: format toggle button (OpenPencil / Tailwind)
- Rename Jsx→JSX in all public APIs (sceneNodeToJSX, selectionToJSX, renderJSX, etc.)
- 29 new Tailwind export tests, all 43 export tests pass
* Extract escapeJSXText — replace nested ternary with entity map lookup
* Deduplicate export-jsx: extract shared padding, corner radius, and node context helpers
* Update changelog
* Tighten Tailwind JSX export fidelity
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