Limit sales product tiles and illustrate categories

[sridharkalaibala]

The sales screen now displays at most 48 product tiles per page, with touch-sized Previous/Next controls and search across the complete catalogue. Category tiles retain uploaded images and otherwise show relevant bundled illustrations.

Validation: 4,123 local tests passed, 2 skipped; frontend production build and attribution checks passed. The staging browser verified pagination and category artwork. Production package prepared with the existing payment extension rc34 preserved.

[github-actions]

Merged to develop. Anyone can test this - you do not need write access.

Try it at https://develop.posnic.io, or run it yourself:

git fetch origin develop && git checkout develop
npm install && npm --prefix api install
npm run dev   # then http://localhost:3000

When you have tested it, say what you did and what happened, and set
QA passed or QA failed. If you cannot set labels, just comment -
a maintainer will.

Reporting that something is broken is as useful as fixing it. It is
better found here than by a shopkeeper.