feat: enrich invoice summary with session payments, consumables and discount

Port the remaining gap of tauri /files/invoice-summary into the admin
invoice summary: GET /api/v1/billing/invoices/{uuid} now includes a
'session' key (full PatientSession payload) so InvoiceSummaryModal can
render the consumables table, the itemized payments table (method,
amount, date-time, recorder) and real discount/paid/remaining figures
instead of heuristics. Invoices without a source session keep the
previous behavior (session: null).

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

src/Billing/Controller/BillingController.php

@@ -139,7 +139,7 @@ class BillingController extends BaseController
             return $this->error(ErrorCodes::ERR_NOT_FOUND_001, 'صورتحساب یافت نشد', 404);
         }
 
-        return $this->success(['data' => $invoice->toArray()]);
+        return $this->success(['data' => $this->invoiceService->detailWithSession($invoice)]);
     }
 
     #[Route('/api/v1/billing/invoices/{uuid}/finalize', methods: ['POST'])]