feat: implement cursor-based pagination across list endpoints

[Thosine-01]

Summary

Implements cursor-based pagination across list endpoints to prevent full-table scans on large datasets and improve API scalability.

Changes

New files

• src/common/dto/pagination.dto.ts — reusable cursor pagination DTO
• src/modules/submissions/dto/query-submission.dto.ts — submissions pagination query DTO
• BackEnd\src\database\migrations\1746000000000-add-cursor-pagination-indexes.ts
• BackEnd\test\pagination\cursor-pagination.e2e-spec.ts

Updated files

• src/modules/quests/* — updated quest list endpoints and services for cursor pagination
• src/modules/users/* — updated leaderboard pagination logic
• src/modules/submissions/submissions.controller.ts
• src/modules/submissions/submissions.service.ts
• src/modules/payouts/payouts.controller.ts
• src/modules/payouts/payouts.service.ts
• src/modules/payouts/dto/payout-query.dto.ts
• src/modules/notifications/notifications.service.ts

Pagination updates

• Replaced page/limit pagination with cursor-based pagination
• Added cursor and limit query support
• Standardized paginated responses with:
  • total
  • limit
  • nextCursor
• Updated Swagger decorators and API query documentation
• Refactored service-layer list queries to support cursor traversal

Performance improvements

• Optimized list queries using createdAt DESC
• Reduced risk of full-table scans on large datasets
• Prepared services for indexed cursor lookups

Notes

Database index migration and pagination e2e tests are still pending and will be added in a follow-up PR.

Breaking changes

• Page-based pagination (page) has been replaced with cursor-based pagination (cursor) on list endpoints.
• Response structure now returns nextCursor instead of page and totalPages.

close #245

[RUKAYAT-CODER]

kindly resolve conflict

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