Load sales shelves on demand and distinguish category illustrations

[sridharkalaibala]

The sales shelf previously downloaded the entire catalogue before displaying its first 48 tiles. Fetch one server page at a time for Items and category browsing, keep variant families together, and use the full-catalogue search endpoint for names and barcodes. Ignore stale page responses and keep existing products visible while loading or retrying a page.

Category tiles also receive distinct illustrations for 66 retail labels, with uploaded images retaining priority.

Validation: 4,125 local tests passed, 2 skipped; two additional real-MongoDB tests passed for page boundaries, scope, variant families, and barcode lookup beyond page one. API controller/repository unit tests (305), language checks (57), frontend build, lint and attribution checks passed. Staging browser network inspection confirmed one page request on Next, plus successful search for an unloaded item and category navigation.

[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.