Fix retail VAT rounding and organise inventory settings

[sridharkalaibala]

Fixes a retail VAT rounding mismatch where two products displayed at £1 could become £1.99. The signed inclusive-price workflow now carries the same gross-unit rounding policy through catalogue preparation, saved pricing and settlement. Normal exclusive-price behavior remains unchanged. Quantity edits also recalculate on input, including pasted values.

Inventory preferences and expiry reminders now live in Manage → Core Settings → Inventory, with separate subsections. Inventory navigation uses Expiry list and Low stock list; existing item-settings links redirect to Core Settings.

Validation:

• Root suite: 4,107 passed, two skipped; its sole missing Dutch translation failure was fixed and the six translation tests passed on rerun.
• API pricing/tax Jest: 21 passed. Real Mongo extension payment integration: 24 passed, including two £1 items settled as £1 cash + £1 card with one stock deduction.
• Final targeted rounding/parity/quantity tests: 16 passed. Frontend build, packaged modules, attribution and diff checks passed. API lint has no errors (21 existing warnings).
• Deployed candidate tested in the built-in browser: two £1 items total £2, eight total £8; £8 synthetic sale recorded £6 cash + £2 card; expiry settings save/reload and navigation verified.

Demo: https://basket-review-test.posnic.com/public/dashboard.html#/settings/general
Companion private extension rc.32 fixes cash-received defaults when the split portion changes. Production is not updated by this PR. Promote develop to main after review, then deploy the matching core and signed extension package.

[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.