Add transfer tracking and secure admin access

backend/MiaoJiZhang.Api.Tests/PushIntegrationTests.cs

@@ -11,8 +11,6 @@ namespace MiaoJiZhang.Api.Tests;
 [Collection(ApiCollection.Name)]
 public sealed class PushIntegrationTests(ApiFixture fixture)
 {
-    private const string AdminKey = "test-only-admin-key-at-least-24-characters";
-
     [Fact]
     public async Task Preferences_DefaultOff_AndPersistAllCategories()
     {
@@ -149,8 +147,7 @@ public sealed class PushIntegrationTests(ApiFixture fixture)
         var userId = profile.GetProperty("userId").GetInt64();
         await RegisterDeviceAsync(user, Guid.NewGuid().ToString(), "campaign-device-token");
 
-        using var admin = fixture.Factory.CreateClient();
-        admin.DefaultRequestHeaders.Add("X-Admin-Key", AdminKey);
+        using var admin = await fixture.AdminAsync();
         var request = new
         {
             title = "系统维护通知",