feat: add OG social images for Triviaverse, Spark, and Game Night

feat: add dynamic next/og social share image tile

feat: cinematic landing page with 3D title, scroll easter egg, and starfield preservation

fix: address code review findings (RLS delete policy, Starfield context, achievement toasts)

feat: add cosmetic definitions, theme system, queries, and CosmeticProvider

fix: move star data to module-level constant, use Tailwind blur classes, add reduced-motion

feat: add starfield background and decorative gradient blobs to root layout

feat: scaffold Next.js 15 + Tailwind v4 + Vitest + Supabase deps