feat: Add Stripe payment integration and subscription management

- Add Stripe.net SDK for payment processing
- Implement StripeService with checkout sessions, customer portal, webhooks
- Implement SubscriptionService for quota management
- Add quota enforcement to CVCheckService
- Create Pricing, Billing, Settings pages
- Add checkout success/cancel pages
- Update Check and Dashboard with usage indicators
- Add ResetMonthlyUsageJob for billing cycle resets
- Add database migration for subscription fields

Plan tiers: Free (3 checks), Professional £49/mo (30), Enterprise £199/mo (unlimited)

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

tests/TrueCV.Tests/Services/CVCheckServiceTests.cs

@@ -24,6 +24,7 @@ public sealed class CVCheckServiceTests : IDisposable
     private readonly Mock<IFileStorageService> _fileStorageServiceMock;
     private readonly Mock<IBackgroundJobClient> _backgroundJobClientMock;
     private readonly Mock<IAuditService> _auditServiceMock;
+    private readonly Mock<ISubscriptionService> _subscriptionServiceMock;
     private readonly Mock<ILogger<CVCheckService>> _loggerMock;
     private readonly CVCheckService _sut;
 
@@ -37,13 +38,19 @@ public sealed class CVCheckServiceTests : IDisposable
         _fileStorageServiceMock = new Mock<IFileStorageService>();
         _backgroundJobClientMock = new Mock<IBackgroundJobClient>();
         _auditServiceMock = new Mock<IAuditService>();
+        _subscriptionServiceMock = new Mock<ISubscriptionService>();
         _loggerMock = new Mock<ILogger<CVCheckService>>();
 
+        // Setup subscription service to allow checks by default
+        _subscriptionServiceMock.Setup(x => x.CanPerformCheckAsync(It.IsAny<Guid>()))
+            .ReturnsAsync(true);
+
         _sut = new CVCheckService(
             _dbContext,
             _fileStorageServiceMock.Object,
             _backgroundJobClientMock.Object,
             _auditServiceMock.Object,
+            _subscriptionServiceMock.Object,
             _loggerMock.Object);
     }