refactor: unify shared UI with runtime theme tokens

[SunilKumarKV]

Summary

• make runtime theme CSS variables the canonical styling source for shared shell surfaces and UI primitives
• refactor shared panels, buttons, badges, inputs, and studio chrome to consume semantic theme variables instead of hard-coded visual classes
• extend runtime/export tests to cover derived semantic variables and preserve existing theme export behavior

Validation

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

Closes #79