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>

src/TrueCV.Web/Components/Pages/Dashboard.razor

@@ -4,6 +4,7 @@
 @implements IDisposable
 
 @inject ICVCheckService CVCheckService
+@inject ISubscriptionService SubscriptionService
 @inject NavigationManager NavigationManager
 @inject AuthenticationStateProvider AuthenticationStateProvider
 @inject ILogger<Dashboard> Logger
@@ -18,6 +19,30 @@
         <div>
             <h1 class="fw-bold mb-1">Dashboard</h1>
             <p class="text-muted mb-0">View and manage your CV verification checks</p>
+            @if (_subscription != null)
+            {
+                <div class="mt-2">
+                    @if (_subscription.IsUnlimited)
+                    {
+                        <span class="badge bg-success-subtle text-success px-3 py-2">
+                            Enterprise - Unlimited checks
+                        </span>
+                    }
+                    else
+                    {
+                        var percentage = _subscription.MonthlyLimit > 0
+                            ? Math.Min(100, (_subscription.ChecksUsedThisMonth * 100) / _subscription.MonthlyLimit)
+                            : 0;
+                        <span class="badge @(percentage >= 90 ? "bg-danger-subtle text-danger" : percentage >= 75 ? "bg-warning-subtle text-warning" : "bg-primary-subtle text-primary") px-3 py-2">
+                            @_subscription.Plan: @_subscription.ChecksUsedThisMonth / @_subscription.MonthlyLimit checks used
+                        </span>
+                        @if (_subscription.ChecksRemaining <= 0)
+                        {
+                            <a href="/pricing" class="btn btn-sm btn-warning ms-2">Upgrade</a>
+                        }
+                    }
+                </div>
+            }
         </div>
         <div class="d-flex gap-2">
             <button class="btn btn-outline-secondary" @onclick="ExportToPdf" disabled="@(_isExporting || !HasCompletedChecks())">
@@ -486,6 +511,7 @@
     private bool _isDeleting;
     private string? _errorMessage;
     private Guid _userId;
+    private SubscriptionInfoDto? _subscription;
     private System.Threading.Timer? _pollingTimer;
     private volatile bool _isPolling;
     private volatile bool _disposed;
@@ -579,6 +605,7 @@
             }
 
             _checks = await CVCheckService.GetUserChecksAsync(_userId) ?? [];
+            _subscription = await SubscriptionService.GetSubscriptionInfoAsync(_userId);
         }
         catch (Exception ex)
         {