Switch to cursor pagination for API

### Describe the problem

The API pagination currently always counts all objects. This can be slow in many situations. The similar issue exists with using offset.

### Solution brainstorm

These kind of problems are typically solved by using cursor pagination instead. DRF already has `CursorPagination` implementation: https://www.django-rest-framework.org/api-guide/pagination/#cursorpagination

### Describe alternatives you have considered

_No response_

### Screenshots

_No response_

### Additional context

This will be a breaking change for some API consumers.

The issue points to Django REST Framework's CursorPagination documentation; start by tracing the existing API pagination configuration and the endpoints that currently count or use offsets. Define the affected API surface and verify that pagination follows cursor semantics, with the breaking-change impact for consumers accounted for.

Written by the indexing model from the issue text.