a11y(website): fix color contrast failures (WCAG 2.1 AA)

[ajitpratap0]

Problem

Nav links and other secondary text use text-zinc-400 (~#a1a1aa) on dark backgrounds, achieving ~3.5:1 contrast ratio. WCAG 2.1 AA requires 4.5:1 for normal text.

axe-core reported 19 affected nodes on the docs page alone.

Affected elements:

• Nav links (Docs, Playground, Blog…)
• Breadcrumb text
• Code panel labels (query.sql, AST Output)
• Footer links

Fix

Change secondary text elements to text-zinc-300 or lighter. Specifically update nav links, breadcrumbs, code panel labels, and footer text from text-zinc-400/text-zinc-500 to text-zinc-300 on dark backgrounds.