perf(search): paginate SearchResults to cap mounted cards per page

[AvatarMiiDe]

## Description

`SearchResults` previously rendered the entire result set into a CSS grid at once — mounting every card and its external image with no limit, causing layout jank on broad queries returning hundreds of courses.

This PR adds client-side pagination to cap the number of cards mounted per render:

- Results are sliced to `pageSize` items (default **12**) per page
- A Prev / Next pagination bar with a "Page N of M" indicator is rendered below the grid when `totalPages > 1`
- The static "Z results found" counter is replaced with a dynamic "Showing X–Y of Z results" range
- Page resets to 1 automatically via `useEffect` whenever the `results` prop changes (new search / filter)
- Two new optional props (`pageSize`, `initialPage`) are fully backward-compatible — all existing callers are unaffected
- 29 unit tests added in `SearchResults.test.tsx` covering slice correctness, navigation, boundary states, page reset, and sort controls

## Related Issue

Closes #

## Type of Change

- [x] Bug fix
- [ ] New feature
- [ ] Breaking change
- [ ] Documentation update

## Checklist

- [x] Code follows project style guidelines
- [x] Self-review completed
- [x] No console errors
- [x] Uses Lucide icons consistently (`ChevronLeft`, `ChevronRight` for pagination; existing icons preserved)
- [x] Responsive design implemented (pagination bar is flex-centered, grid remains 1/2/3-col responsive)
- [ ] Starknet best practices followed (not applicable — UI-only change)


Close #941

[drips-wave]

@AvatarMiiDe Great news! 🎉 Based on an automated assessment of this PR, the linked Wave issue(s) no longer count against your application limits.

You can now already apply to more issues while waiting for a review of this PR. Keep up the great work! 🚀

Learn more about application limits

[RUKAYAT-CODER]

Well done on the job done!
Kindly fix workflow to pass