feat(api): implement pagination for NCERT chapter browsing endpoints (#526)

[Rajen5145]

Closes #526

Overview

Implements database-level pagination for NCERT chapter browsing endpoints to ensure scalable performance, prevent slow load times, and reduce frontend rendering overhead as the academic structure seed data grows.

Summary of Changes

• Database Query & Pagination:
  • Utilized Prisma's skip (offset) and take (limit) methods in NcertRepository.getChapters to fetch chapter results in paginated chunks.
  • Added structured pagination metadata including currentPage, totalItems, totalPages, limit, and total.
• API Standardization:
  • Handled page and limit query parameters with fallback defaults (page=1, limit=20) to prevent unconstrained full-table scans.
• Frontend Data Fetching:
  • Updated NCERT browsing endpoints in src/app/ncert/[class]/[subject]/page.tsx and src/app/ncert/[class]/[subject]/[chapter]/page.tsx to pass default pagination query parameters (?page=1&limit=20).

Testing & Verification

• Verified that API responses return proper metadata matching the total database count.
• Verified backwards compatibility with existing UI components consuming chapter data.

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