docs: README + description.md

README covers:
- What the extension is / isn't (CMS only; customer UI in webapp;
  no festival entity; no central splitter)
- Architecture diagram
- Data model summary
- Order state machine
- Nostr (kind 0 / 30402 / 5; NIP-17 stub)
- Public vs owner-write API surface
- A worked-out webapp integration snippet showing the multi-
  restaurant cart flow (group by restaurant -> per-restaurant
  quote -> sufficient-balance check -> N place_order calls ->
  pay each bolt11)
- Install instructions for development
- Roadmap of explicitly-deferred items (NIP-44 unwrap, per-
  restaurant secret storage, SSE/push, HODL atomicity, foreign
  menu cache, image upload pipeline)

description.md

@@ -0,0 +1,9 @@
+Restaurant CMS for LNbits. Build menus, manage modifiers and inventory,
+and process Lightning orders. Menus are published to Nostr (NIP-99
+classified listings) so customer-facing webapps and aggregators
+(festivals, food courts, collective spaces) can subscribe live across
+many restaurants. Each restaurant issues its own invoice — multi-
+restaurant carts pay each restaurant directly, no central wallet, no
+splitting. Includes a Kitchen Display screen, thermal printer queue,
+and an order state machine (pending → paid → accepted → ready →
+completed).