feat(discount): apply a discount rule to a session with audit

Extend PatientService::applyDiscount to carry the source rule id/label and
add applyDiscountRule, which computes the rial amount via the engine
(DiscountEngine::computeForRule now public) and records the rule for audit.
updateSession accepts discount_rule_uuid (owner-scoped, takes precedence over
the manual discount; ''/null clears). Verified end-to-end.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

src/Patient/Controller/PatientController.php

@@ -60,6 +60,7 @@ class PatientController extends BaseController
         private readonly \App\Settlement\Repository\WalletTransactionRepository $walletRepo,
         private readonly \App\Settlement\Repository\SettlementRepository $settlementRepo,
         private readonly \App\Settlement\Service\WalletService $walletService,
+        private readonly \App\Discount\Repository\DiscountRuleRepository $discountRuleRepo,
         private readonly LoggerInterface             $logger,
     ) {}
 
@@ -1046,8 +1047,21 @@ class PatientController extends BaseController
 
         if (isset($data['notes'])) { $session->setNotes($data['notes']); }
 
-        // تخفیف تسویه: discount_type = percent|fixed|null (null = حذف تخفیف)
-        if (array_key_exists('discount_type', $data)) {
+        // تخفیف بر اساس قانون (discount_rule_uuid): مقدار از خود قانون، با ثبت منبع.
+        // '' یا null → حذف تخفیف. اولویت بر تخفیف دستی.
+        if (array_key_exists('discount_rule_uuid', $data)) {
+            $ruleUuid = $data['discount_rule_uuid'];
+            if ($ruleUuid === null || $ruleUuid === '') {
+                $this->patientService->applyDiscount($session, null, 0);
+            } else {
+                $rule = $this->discountRuleRepo->findByUuidForOwner((string) $ruleUuid, $entityType, $entityId);
+                if ($rule === null) {
+                    return $this->error(ErrorCodes::ERR_VALIDATION_002, 'قانون تخفیف یافت نشد', 404, 'discount_rule_uuid');
+                }
+                $this->patientService->applyDiscountRule($session, $rule);
+            }
+        } elseif (array_key_exists('discount_type', $data)) {
+            // تخفیف دستی: discount_type = percent|fixed|null (null = حذف تخفیف)
             $type = $data['discount_type'] !== null ? (string) $data['discount_type'] : null;
             $this->patientService->applyDiscount($session, $type, (int) ($data['discount_value'] ?? 0));
         }