feat: build Theme Studio V2

[SunilKumarKV]

Summary

• add six typed theme presets with live runtime switching on the existing theme engine
• expand Theme Studio with typography and spacing controls, validated theme.json import, and production exports
• rebuild the Theme Studio workspace around real RainbowCode previews for navbar, sidebar, button, input, card, and dashboard surfaces
• add preset, import/export, store, and preview render coverage plus founder QA and release reports

Validation

• pnpm typecheck
• pnpm lint
• pnpm test
• pnpm build

Closes #81