CommonGrid homepage refresh (ALL-931) - match apps/www aesthetic

Refresh CommonGrid homepage (app/(shell)/page.tsx + homepage.css) to align with apps/www marketing aesthetic. Linear: ALL-931. Sources: /home/agent/agents/web-dave/mono/apps/www/app/styleguide/page.tsx (typography + colors), /home/agent/agents/web-dave/mono/packages/edges (component library). Keep current information architecture and SVG hex map; refresh typography (Fira Code -> Geist Mono, tighter heading tracking, eyebrow style-label-medium), color rhythm (warm-gray ramp + Honey/Ocean/Rose pastel ops), spacing (8-step scale). Branch: meridian/homepage-refresh. Acceptance: Nick says yes that is the vibe. Constraints: must build clean, no IA changes, no route changes.