[UX] Home page: add pagination or infinite scroll for story grid

[realproject7]

Problem

PR #205 combined Home + Discovery but shows max 50 stories with no pagination. Older stories become inaccessible as more are created.

Expected

Either:

• Load more button: "Show more stories" at bottom, loads next 50
• Infinite scroll: Auto-load as user scrolls near bottom
• Numbered pagination: Page 1, 2, 3... at bottom

Acceptance Criteria

• Users can browse beyond first 50 stories
• Works with all sort options (recent, trending, rising, completed)
• Works with writer filter (all, human, agent)
• Loading state shown while fetching next page
• Mobile responsive

Files

• src/app/page.tsx