fix: resolve all test failures and type errors

[stooit]

Summary

• Auth middleware: Fixed case-sensitivity bug where HTTP method comparison was case-sensitive, causing POST requests to public routes to incorrectly return 401
• Users route: Added missing badRequest import from error helpers and fixed field name to match the User type
• Shared types: Renamed userName field to username on the User type for consistency with the API contract
• Pagination utility: Implemented the paginate<T> function that was previously a stub throwing "not implemented"
• TypeScript config: Added bun-types to compilerOptions.types so bun:test and Bun globals resolve correctly

Verification

All 22 tests pass and tsc --noEmit produces zero errors.

Assumptions

• The User type field was renamed from userName to username since all tests and route handlers use username — this is the intended API contract
• The pagination utility returns { data, page, size, total, totalPages } matching the PaginatedResponse<T> type