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/Insurance/ValueObject/CoverageRule.php

@@ -0,0 +1,18 @@
+<?php
+
+namespace App\Insurance\ValueObject;
+
+final readonly class CoverageRule
+{
+    public function __construct(
+        public float $coveragePercent,
+        public int   $franchiseRials,
+        public ?int  $ceilingRials,
+        public bool  $covered = true,
+    ) {}
+
+    public static function notCovered(): self
+    {
+        return new self(0.0, 0, null, false);
+    }
+}