fix(market): declare feeMsat on Order so the persisted fee is typed

`useLightningPayment` writes feeMsat onto the paid order, but `Order`
never declared it. `updateOrder` takes `Partial<Order>`, and the write
goes through an inferred variable, so the excess-property check never
fired — the value landed in the store invisible to the type system and
unreadable by any consumer.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>

src/modules/market/types/market.ts

@@ -129,6 +129,7 @@ export interface Order {
   originalOrderId?: string
   lightningInvoice?: any
   paymentHash?: string
+  feeMsat?: number  // Routing fee paid on the Lightning payment, in millisats
   paidAt?: number
   paymentStatus?: 'pending' | 'paid' | 'expired'
   paid?: boolean  // Direct boolean field matching nostrmarket reference