Refactor: Replace inline styles with tokenized CSS classes across docs UI

[hdcodedev]

Summary

Refactor inline styles into semantic classes and design-token-driven CSS.

Why

Inline styles are scattered across pages/components and bypass the design system, making consistency harder.

Scope

• Remove inline styling from docs API page, 404 page, and interactive controls where present.
• Introduce component-level classes in globals.css (or split CSS modules if preferred).
• Ensure all visual values come from shared tokens when possible.

Acceptance Criteria

• Target components no longer rely on inline style objects for core styling.
• New classes are named and documented consistently.
• Visual output remains functionally equivalent or improved.

[hdcodedev]

Closed — addressed or superseded by modernization work in #44.