Give mobile inventory its own settings menu and default access

[sridharkalaibala]

Mobile inventory was hidden inside Expiry reminders. Give it its own Core Settings → Inventory → Mobile inventory menu, and default it on for new branches and branches without a saved choice. Preserve explicit opt-outs, staff ACL and existing manager-approval actions. No stock is changed by enabling access.

Validation: 41 API tests passed, 5 optional full-app tests skipped; browser DOM check confirmed the dedicated menu, default-enabled checkbox and retained approval choice; 5 sync classification tests passed; attribution and JavaScript syntax checks passed. API files formatted. Live device and cloud/till sync delivery have not been verified.

Sync: continues using branches.inventory_policy and updated_date on the existing POS/Gateway global branch classification and agent batch lane; no new data lane or journal replication. API and frontend should deploy together and connected tills need the same default interpretation. No APK update required. Rollout details are in docs/MOBILE_INVENTORY_IMPLEMENTATION.md.

[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.