Improve inventory icons and restock supplier selection

[sridharkalaibala]

Inventory navigation uses distinct icons. Restock quantities have large minus/plus controls in a wider responsive dialog.

When restock items have no assigned supplier, the purchase selector now searches the branch supplier directory. Selecting a supplier transfers its items plus unassigned items into the purchase, while other supplier groups remain in the basket. The selected supplier name and details carry into the purchase form.

Validation: eight restock tests passed, covering quantity bounds, unassigned supplier handoff, preserving other supplier groups and existing purchases. Frontend build, formatting, diff and attribution checks passed. Browser verified Gene finds General Supplier with only an unassigned item, and supplier plus quantity transfer correctly. The unsaved test purchase was cleared. Production unchanged.

[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.