feat(online): server-side ordering, pagination, and load-more fix

[RomainFleury]

Note: I am not a python developer so there are quite some things that I might have missed. The behaviour seems ok:

• infinite scroll
• filters being applied (new/old, most downloaded, most liked)
• search
• and the roulette has been changed a bit to use a new api entry point that I added

Description

Server-side ordering and pagination for the Online tab so the list matches the website and "Load more" works correctly.

• API integration: Use orderBy (latest/oldest/like/download) and hasNextPage; get_character_list returns (rows, has_next_page).
• Scraper/workers: Pagination-only fetch; ScraperWorker supports order_by and multi-page initial load.
• Online tab: Sort order matches the website by trusting API order for server-side sorts and refetching when the user changes to Date/Most Downloaded/Most Liked; Name A–Z remains client-side.
• Load more: Button stays visible when the API reports more pages; last_fetched_api_page tracks which page to request next so we don't re-request already-fetched pages.
• Roulette: Fetches 5 random characters from the API and refetches on "GIRAR DE NUEVO".
• Docs: Added docs/API-INTEGRATION.md for API usage.

Fixes the list appearing "stuck" after the first few pages and ensures sort order matches star-citizen-characters.com.

Type of change

• New feature (non-breaking change which adds functionality)
• Bug fix (non-breaking change which fixes an issue – load more / sort mismatch)

Checklist

• My code follows the style guidelines of this project (flake8)
• I have performed a self-review of my own code
• I have made corresponding changes to the documentation (docs/API-INTEGRATION.md)
• My changes generate no new warnings
• I have added tests that prove my fix is effective or that my feature works (existing tests pass; no new tests for online tab)