feat: add server-side pagination to leaderboard page (#637)

[Shiva210Jyoti]

Resolves #637

Summary

Implements server-side pagination for the leaderboard page using Drizzle ORM with raw SQL OFFSET/LIMIT queries.

Changes

src/app/actions/getLeaderboardPage.ts (new)

• New server action getLeaderboardPage(page, pageSize = 20)
• Orders profiles by XP descending with LIMIT/OFFSET
• Returns { entries, totalCount, page, pageSize }
• Global rank: (page - 1) * pageSize + index + 1

src/app/(app)/leaderboard/page.tsx

• Reads page from searchParams (Next.js server component, no client state)
• Global scope uses getLeaderboardPage, other scopes use existing getLeaderboard
• Resolves current user rank across pages

src/app/(app)/leaderboard/leaderboard-content.tsx

• Shows {N} CONTRIBUTORS above the table
• Highlights current user row via entry.userId === currentUserId
• Prev/Next as <Link href="?page=n"> matching Issues page pagination style
• Podium shown on page 1 only

Acceptance Criteria

Requirement	Status
Default page size 20	✅
Global rank numbers across pages	✅
URL-based pagination ?page=n	✅
Current user highlighted across pages	✅
Total contributor count above table	✅
Server-side pagination (not client slice)	✅
Prev/Next consistent with Issues page	✅
Podium only on page 1	✅

Notes

• Repo uses Drizzle + raw SQL, not Prisma — same pagination concept with skip/take equivalent
• Build clean, tsc --noEmit clean on leaderboard files

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[Shiva210Jyoti]

Hey @jakharmonika364 @Ayush-Patel-56, PR #703 is ready for review! All acceptance criteria covered, build clean. Please take a look 🙏

[jakharmonika364]

order by xp desc has no tiebreaker, so ties (very common at low xp) aren't stable across separate page loads - a contributor can show up on two pages or vanish from all of them. add order by xp desc, id asc.

also this bypasses getLeaderboard entirely for the global scope, so it has no rate limit (see #688) and no cache, unlike the sibling it duplicates. and rank here is row position, not dense_rank like every other scope uses, so tied users get different ranks.