User guide: fix annotation placement on Inventory and Custom Units screenshots

Highlight boxes are now drawn after the viewport is resized to the page height, so they sit on their targets (right-edge buttons were previously offset). Also: the Custom Units request-history image now shows a request with units, and the distribution-from-request image calls out the quantity field next to the requested packs.

Co-Authored-By: Claude Fable 5.1 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01LMAt57FU2qBq45yR7YCsEZ

Author: awwaiid