refactor: restructure API pagination metadata for better frontend usability

- Create PaginationMetadata model with computed derived fields (total_pages, has_next_page, has_prev_page)
- Update PaginatedListResponse to embed pagination metadata in a separate 'pagination' object
- Add create_pagination_metadata() factory function in utils/pagination.py for consistent computation
- Update all paginated service functions to use new structure:
  - history_service.list_history()
  - blocklist_service.get_import_logs()
  - jail_service.get_jail_banned_ips()
  - ban_mappers.map_domain_dashboard_ban_list_to_response()
- Update response model docstrings with new structure examples
- Update Backend-Development.md documentation with new pagination patterns
- Update test fixtures to work with new response structure

Response shape changes from:
  {"items": [...], "total": 100, "page": 1, "page_size": 50}
To:
  {"items": [...], "pagination": {"page": 1, "page_size": 50, "total": 100, "total_pages": 2, "has_next_page": true, "has_prev_page": false}}

Benefits:
- Frontend receives all pagination state needed for UI controls
- No need for frontend to calculate total_pages or page navigation logic
- Consolidated pagination metadata reduces field sprawl
- OpenAPI schema automatically reflects changes

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

backend/app/mappers/ban_mappers.py

@@ -28,6 +28,7 @@ from app.models.ban_domain import (
     DomainDashboardBanItem,
     DomainDashboardBanList,
 )
+from app.utils.pagination import create_pagination_metadata
 
 
 def map_domain_active_ban_to_response(domain_ban: DomainActiveBan) -> ActiveBan:
@@ -78,9 +79,7 @@ def map_domain_dashboard_ban_list_to_response(
         items=[
             map_domain_dashboard_ban_item_to_response(item) for item in domain_list.items
         ],
-        total=domain_list.total,
-        page=domain_list.page,
-        page_size=domain_list.page_size,
+        pagination=create_pagination_metadata(domain_list.total, domain_list.page, domain_list.page_size),
     )