feat: insurance & medical billing system (6 phases)

Multi-tenant insurance contracts, service coverage, versioned tariffs,
invoice calculation, and insurance claims with debt reporting.

- TenantInsurance: per-tenant insurance contracts (coverage/franchise/ceiling,
  versioning, soft-deactivate) + active guard
- ServiceItem.insuranceCovered + TenantServiceCoverage per-service overrides
- Tariff: versioned yearly tariffs with fallback to ServiceItem price
- Billing domain: Money/ShareBreakdown VOs, BillingCalculator (unit-tested),
  Invoice/InvoiceItem aggregate, InvoiceService.createFromSession
- Claim/ClaimItem with state machine (pending->submitted->approved/rejected->paid),
  ClaimService, insurance-debt report
- ClaimSubmitterInterface + ManualClaimSubmitter (future insurance API ready)
- Admin UI: insurance-pricing page, claims page, service tariff modal,
  service insurance toggle; routes + sidebar entries
- Architecture doc + billing/insurance/clinic-services API docs

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

src/Billing/Repository/InvoiceItemRepository.php

@@ -0,0 +1,23 @@
+<?php
+
+namespace App\Billing\Repository;
+
+use App\Billing\Entity\InvoiceItem;
+use Doctrine\Bundle\DoctrineBundle\Repository\ServiceEntityRepository;
+use Doctrine\Persistence\ManagerRegistry;
+
+class InvoiceItemRepository extends ServiceEntityRepository
+{
+    public function __construct(ManagerRegistry $registry)
+    {
+        parent::__construct($registry, InvoiceItem::class);
+    }
+
+    public function save(InvoiceItem $entity, bool $flush = true): void
+    {
+        $this->getEntityManager()->persist($entity);
+        if ($flush) {
+            $this->getEntityManager()->flush();
+        }
+    }
+}