Replace react-syntax-highlighter with Prism.js after Tailwind migration

Summary

Replace react-syntax-highlighter with prismjs for code syntax highlighting.

Context

As the Tailwind migration progresses and design tokens move from JS objects (colors.primary[500]) to CSS custom properties (var(--color-primary-500)), Prism becomes the better fit:

• Prism themes are CSS classes that naturally reference CSS custom properties / design tokens
• react-syntax-highlighter themes are JS inline styles that can't reference CSS variables without extra plumbing
• Bundle size: Prism is ~6KB vs ~40KB for react-syntax-highlighter
• Precedent: pe-taxsim dashboard already uses Prism with Tailwind + CSS tokens successfully

Blocked by

Tailwind migration completing (design tokens moved to CSS custom properties).

Changes

• Remove react-syntax-highlighter and @types/react-syntax-highlighter dependencies
• Install prismjs
• Replace <SyntaxHighlighter> component usage with Prism's highlight() + CSS theme
• Define Prism token colors using design token CSS variables in the global stylesheet

First verify that the Tailwind migration and design-token move are complete, then locate all SyntaxHighlighter usages, the dependency manifests, and the global stylesheet. Replace the component integration and define Prism token colors with CSS custom properties; done when react-syntax-highlighter and its types are removed, Prism is installed, and highlighting works with the migrated tokens.