[Layout] Combine Home + Discovery into single page with grid and sort/filter

[realproject7]

Home and Discovery pages are separate but redundant. Combine into single Home page with: hero, filter bar (All/Human/AI), sort dropdown (Recent/Popular/Rising), responsive story grid (2-3 cols desktop, 1 mobile), cards showing title/author/plots/rating/price/preview, pagination or infinite scroll. Remove /discover route (redirect to /). Remove discover from nav bar. Files: src/app/page.tsx, src/app/discover/page.tsx, src/components/NavBar.tsx