Add unit tests for pagination helpers

[todo-mdx]

TESTING: helpers/pagination.ts has 0% test coverage.

Location: src/helpers/pagination.ts

TDD Steps:

• RED: Write tests for: buildPagination() link generation, buildCursorPagination(), edge cases (empty results, single page, last page)
• GREEN: All tests should pass
• REFACTOR: Test off-by-one scenarios