feat: Add debug data seeding trigger via VAT number 12345

- In DEBUG builds only, entering '12345' as VAT number triggers data seeding
- Calls /api/dev/reseed endpoint to seed test data
- Shows user feedback: 'Debug mode: Triggering data seeding...'
- Useful for mobile app testing where backend reseed may be needed
- Only works in debug builds, automatically excluded from release builds

Author: FiftyEightSoftware

ai_mate_blazor/Pages/Onboarding.razor

@@ -4,6 +4,8 @@
 @inject IJSRuntime JS
 @inject ai_mate_blazor.Services.HmrcValidationService HmrcValidation
 @inject NavigationManager Navigation
+@inject HttpClient Http
+@inject IConfiguration Configuration
 
 <div style="max-width: 600px; margin: 40px auto; padding: 20px;">
     <h2 id="onboarding-heading" style="margin-bottom: 24px;">Welcome to AI Mate</h2>
@@ -235,6 +237,37 @@
             return;
         }
 
+        // DEBUG ONLY: Check for magic VAT number "12345" to trigger data seeding
+        #if DEBUG
+        if (VatRegistrationId?.Trim() == "12345")
+        {
+            InfoMessage = "🔧 Debug mode: Triggering data seeding...";
+            StateHasChanged();
+            
+            try
+            {
+                var apiUrl = Configuration["ApiUrl"] ?? "http://localhost:5252";
+                var response = await Http.PostAsync($"{apiUrl}/api/dev/reseed", null);
+                
+                if (response.IsSuccessStatusCode)
+                {
+                    InfoMessage = "✅ Debug data seeded successfully! Redirecting...";
+                }
+                else
+                {
+                    InfoMessage = $"⚠️ Data seeding failed: {response.StatusCode}. Continuing anyway...";
+                }
+            }
+            catch (Exception ex)
+            {
+                InfoMessage = $"⚠️ Data seeding error: {ex.Message}. Continuing anyway...";
+            }
+            
+            StateHasChanged();
+            await Task.Delay(1500);
+        }
+        #endif
+
         // Mark onboarding as complete and persist IDs to localStorage immediately for UI tests
         try { await JS.InvokeVoidAsync("localStorage.setItem", "aimate_onboarding_completed_v1", "1"); } catch { }
         try { await JS.InvokeVoidAsync("localStorage.setItem", "aimate_vat_registration_id_v1", VatRegistrationId ?? ""); } catch { }