Fix stock refresh and held-basket resume after pagination

[sridharkalaibala]

Sales stock tiles stopped refreshing after the catalogue pagination change removed the loader used by extension checkout. Cash sales and stock adjustments reached the server, but the tiles kept their old quantities; resuming a held basket also depended on that removed loader.

Refresh visible products and saved basket products through targeted item reads with bounded concurrency. Ignore stale refresh results after a newer request or branch change, retain the current cart, update variant choices, and show a retryable error when stock cannot be read. Also includes the expiry/low-stock pagination fixes from #1236 so unavailable navigation controls are hidden.

Validation: 18 local core regression tests and attribution check passed; frontend production build passed. Staging UI cash, card and adjustment tests each changed stock from 10 to 9, confirmed against the database. Holding kept stock at 10, resume restored the correct product/quantity, and manual refresh preserved the cart. The 17 extension workflow tests passed, including adjustment deletion without double deduction.

[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.