feat: add Lightning payment endpoints for paid marketplace

- marketplace.create-invoice: generates BOLT11 via LND for app purchase
- marketplace.check-payment: checks invoice settlement status
- Uses existing LND integration (createinvoice/lookupinvoice)

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

core/archipelago/src/api/rpc/mod.rs

@@ -560,6 +560,8 @@ impl RpcHandler {
             "marketplace.get-manifest" => self.handle_marketplace_get_manifest(params).await,
             "marketplace.list-published" => self.handle_marketplace_list_published().await,
             "marketplace.verify" => self.handle_marketplace_verify(params).await,
+            "marketplace.create-invoice" => self.handle_marketplace_create_invoice(params).await,
+            "marketplace.check-payment" => self.handle_marketplace_check_payment(params).await,
 
             // Mesh networking
             "mesh.status" => self.handle_mesh_status().await,