Add Frontdesk-style Devices registry for POS hardware.

Register tills, customer displays, kitchen screens, printers, scanners,
and tablets per branch. Customer displays share the branch display token
and mark online when the public screen polls; stale devices go offline
on a schedule.

README.md

@@ -2,12 +2,13 @@
 
 In-store register at **pos.ladill.com** — product grid, cart, cash or Ladill Pay checkout.
 
-## Features (v1)
+## Features
 
 - **Register** — catalog + quick-amount sales
 - **Products** — local catalog CRUD
 - **Sales** — history and receipt view
-- **Ladill Pay** — MoMo/card via `source_service: pos`, `fee_tier: sales`
+- **Devices** — tills, customer displays, kitchen screens, printers (tokenized where needed)
+- **Payment gateway** — merchant Paystack / Flutterwave / Hubtel (Pro+)
 
 ## Local dev