docs: redesign GitHub Pages with minimal premium dark aesthetic

[Copilot]

Rewrites docs/index.html CSS to match the clean, editorial style of claude.com/product/claude-code. All content, SEO meta, and structure are preserved — style only.

Changes

Palette

• Replaced blue-tinted dark (#0d0f14, borders #2a3347) with warm neutral dark (#0a0a0a, borders #242424)
• Dropped blue+purple gradient accent in favour of single warm orange #d97757

Typography

• Hero h1 scaled up (clamp(2.8rem, 7vw, 4.4rem)) with tighter tracking (-.03em)
• Section headings tighter (-.025em); nav logo plain text, no gradient fill

Hero

• Ambient radial glow (orange, 8% opacity) via ::before pseudo-element
• Vertical padding 120px (was 96px)

Feature grid

• Replaced 20 individually bordered + filled cards with a unified grid divided by hairline separators (gap: 1px on a background: var(--border) wrapper) — more editorial, less widget-heavy

Nav / footer

• GitHub nav link: borderless text with hover transition (no button chrome)
• Footer links: muted-to-white on hover instead of accent colour

Spacing

• Section vertical spacing 100px throughout (was 80px); agent strip, demo, and fullshot sections proportionally more breathable