feat(billing-v2-c): BalancePreflightService — pure-проверка платёжеспособности

Task 1.2 Спека C. evaluate(balanceRub, deliveredInMonth, requiredLeads, tiers) →
PreflightResult{passes, requiredLeads, capacityLeads, deficitLeads}. Сравнение в
лидах через BalanceToLeadsConverter::convert (7 ступеней + месячный объём).
3 unit-теста GREEN. Pint passed.

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

app/tests/Unit/Billing/BalancePreflightServiceTest.php

@@ -0,0 +1,52 @@
+<?php
+
+declare(strict_types=1);
+
+use App\Models\PricingTier;
+use App\Services\Billing\BalancePreflightService;
+use Illuminate\Database\Eloquent\Collection;
+
+function makeTiers(): Collection
+{
+    // 1 ступень: цена 50₽/лид (5000 копеек), безлимитная.
+    return new Collection([
+        new PricingTier(['tier_no' => 1, 'leads_in_tier' => null, 'price_per_lead_kopecks' => 5000, 'is_active' => true]),
+    ]);
+}
+
+it('passes when balance covers full daily limit', function () {
+    $service = new BalancePreflightService;
+    // 2000₽ / 50₽ = 40 лидов capacity; нужно 30 → проходит.
+    $result = $service->evaluate(
+        balanceRub: '2000.00',
+        deliveredInMonth: 0,
+        requiredLeads: 30,
+        tiers: makeTiers(),
+    );
+
+    expect($result->passes)->toBeTrue();
+    expect($result->capacityLeads)->toBe(40);
+    expect($result->requiredLeads)->toBe(30);
+    expect($result->deficitLeads)->toBe(0);
+});
+
+it('fails when balance below full daily limit', function () {
+    $service = new BalancePreflightService;
+    // 1000₽ / 50₽ = 20 лидов capacity; нужно 30 → не проходит, дефицит 10.
+    $result = $service->evaluate(
+        balanceRub: '1000.00',
+        deliveredInMonth: 0,
+        requiredLeads: 30,
+        tiers: makeTiers(),
+    );
+
+    expect($result->passes)->toBeFalse();
+    expect($result->capacityLeads)->toBe(20);
+    expect($result->deficitLeads)->toBe(10);
+});
+
+it('passes trivially when requiredLeads is zero', function () {
+    $service = new BalancePreflightService;
+    $result = $service->evaluate('0.00', 0, 0, makeTiers());
+    expect($result->passes)->toBeTrue();
+});