Refactor: remove unnecessary using directives

Removed unused using statements from page models and test files:
- Removed unused Microsoft.EntityFrameworkCore and MoneyMap.Data imports
- Removed redundant Xunit usings (already declared as global)

Fixes CS8019 and CS8933 hidden diagnostics.

MoneyMap.Tests/Services/AccountServiceTests.cs

@@ -1,7 +1,6 @@
 using MoneyMap.Models;
 using MoneyMap.Services;
 using MoneyMap.Tests.TestHelpers;
-using Xunit;
 
 namespace MoneyMap.Tests.Services;
 

MoneyMap.Tests/Services/CardServiceTests.cs

@@ -1,7 +1,6 @@
 using MoneyMap.Models;
 using MoneyMap.Services;
 using MoneyMap.Tests.TestHelpers;
-using Xunit;
 
 namespace MoneyMap.Tests.Services;
 

MoneyMap.Tests/Services/MerchantServiceTests.cs

@@ -1,7 +1,6 @@
 using MoneyMap.Models;
 using MoneyMap.Services;
 using MoneyMap.Tests.TestHelpers;
-using Xunit;
 
 namespace MoneyMap.Tests.Services;
 

MoneyMap.Tests/Services/ReceiptMatchingServiceTests.cs

@@ -1,7 +1,6 @@
 using MoneyMap.Models;
 using MoneyMap.Services;
 using MoneyMap.Tests.TestHelpers;
-using Xunit;
 
 namespace MoneyMap.Tests.Services;
 

MoneyMap.Tests/Services/ReferenceDataServiceTests.cs

@@ -1,7 +1,6 @@
 using MoneyMap.Models;
 using MoneyMap.Services;
 using MoneyMap.Tests.TestHelpers;
-using Xunit;
 
 namespace MoneyMap.Tests.Services;
 

MoneyMap.Tests/Services/TransactionServiceTests.cs

@@ -1,7 +1,6 @@
 using MoneyMap.Models;
 using MoneyMap.Services;
 using MoneyMap.Tests.TestHelpers;
-using Xunit;
 
 namespace MoneyMap.Tests.Services;
 

MoneyMap.Tests/Services/TransactionStatisticsServiceTests.cs

@@ -1,7 +1,6 @@
 using MoneyMap.Models;
 using MoneyMap.Services;
 using MoneyMap.Tests.TestHelpers;
-using Xunit;
 
 namespace MoneyMap.Tests.Services;