Remove FluentValidation; validator/DI cleanup (#7)

## Summary
- Remove FluentValidation dependency; replace with plain IModelValidator<T>/ValidationResult pattern (ported from BuyEngine's Guard/validation approach), wired via a ModelValidationActionFilter
- Move FeatureUsage code into MicCheck.Api.Features.Usage namespace
- Convert logic-free data classes to records per CLAUDE.md (WebhookEvent, FeatureStateResult, ProjectPermissionRequirement, AuditLog, Tag, FeatureUsageDaily)
- Extract IAuditService interface, drop virtual-method mock seam on AuditService
- Split Program.cs DI registrations into per-namespace DependencyRegistration classes

## Test plan
- [x] dotnet build (API + tests) clean
- [x] dotnet test MicCheck.Api.Tests.Unit — 646/646 passing
- [x] pre-push hook (full solution build/test + admin build) passed

Co-authored-by: miccheck-ci <ci@miccheck.local>
Reviewed-on: #7

tests/api/MicCheck.Api.Tests.Unit/Admin/AdminApiIntegrationTests.cs

@@ -23,7 +23,7 @@ public class AdminApiIntegrationTests
     private List<FeatureState> _featureStates = null!;
     private List<AppEnvironment> _environments = null!;
     private List<Segment> _segments = null!;
-    private Mock<AuditService> _auditService = null!;
+    private Mock<IAuditService> _auditService = null!;
     private int _organizationId;
 
     [SetUp]
@@ -50,7 +50,7 @@ public class AdminApiIntegrationTests
         _db.SetupDbSetWithGeneratedIds(c => c.SegmentConditions, []);
 
         var webhookQueue = new WebhookQueue();
-        _auditService = new Mock<AuditService>(_db.Object, null!, webhookQueue);
+        _auditService = new Mock<IAuditService>();
         _auditService.Setup(a => a.LogAsync(
             It.IsAny<string>(), It.IsAny<string>(), It.IsAny<string>(),
             It.IsAny<int>(), It.IsAny<int?>(), It.IsAny<int?>(),

tests/api/MicCheck.Api.Tests.Unit/Audit/AuditLogsControllerTests.cs

@@ -46,7 +46,7 @@ public class AuditLogsControllerTests
         _db.SetupDbSet(c => c.AuditLogs, _auditLogs);
         _db.SetupDbSet(c => c.Users, []);
 
-        var auditServiceMock = new Mock<AuditService>(_db.Object, null!, new MicCheck.Api.Webhooks.WebhookQueue());
+        var auditServiceMock = new Mock<IAuditService>();
         var auditService = auditServiceMock.Object;
 
         _controller = new AuditLogsController(

tests/api/MicCheck.Api.Tests.Unit/Environments/EnvironmentServiceTests.cs

@@ -45,7 +45,7 @@ public class EnvironmentServiceTests
         _db.SetupDbSet(c => c.Identities, _identities);
 
         var webhookQueue = new MicCheck.Api.Webhooks.WebhookQueue();
-        var auditService = new Mock<AuditService>(_db.Object, null!, webhookQueue);
+        var auditService = new Mock<IAuditService>();
         auditService.Setup(a => a.LogAsync(
             It.IsAny<string>(), It.IsAny<string>(), It.IsAny<string>(),
             It.IsAny<int>(), It.IsAny<int?>(), It.IsAny<int?>(),

tests/api/MicCheck.Api.Tests.Unit/Environments/EnvironmentsControllerTests.cs

@@ -113,7 +113,7 @@ public class EnvironmentsControllerTests
         _db.SetupDbSet(c => c.Users, []);
 
         var webhookQueue = new WebhookQueue();
-        var auditServiceMock = new Mock<AuditService>(_db.Object, null!, webhookQueue);
+        var auditServiceMock = new Mock<IAuditService>();
         auditServiceMock.Setup(a => a.LogAsync(
             It.IsAny<string>(), It.IsAny<string>(), It.IsAny<string>(),
             It.IsAny<int>(), It.IsAny<int?>(), It.IsAny<int?>(),

tests/api/MicCheck.Api.Tests.Unit/Features/FeatureEvaluationServiceTests.cs

@@ -1,6 +1,7 @@
 using System.Diagnostics.Metrics;
 using MicCheck.Api.Data;
 using MicCheck.Api.Features;
+using MicCheck.Api.Features.Usage;
 using MicCheck.Api.Identities;
 using MicCheck.Api.Segments;
 using MicCheck.Api.Tests.Unit.TestSupport;

tests/api/MicCheck.Api.Tests.Unit/Features/FeatureServiceTests.cs

@@ -45,7 +45,7 @@ public class FeatureServiceTests
         _db.SetupDbSetWithGeneratedIds(c => c.Tags, _tags);
 
         var webhookQueue = new MicCheck.Api.Webhooks.WebhookQueue();
-        var auditService = new Mock<AuditService>(_db.Object, null!, webhookQueue);
+        var auditService = new Mock<IAuditService>();
         auditService.Setup(a => a.RecordAsync(
             It.IsAny<string>(), It.IsAny<string>(), It.IsAny<string>(),
             It.IsAny<int>(), It.IsAny<int?>(), It.IsAny<int?>(),

tests/api/MicCheck.Api.Tests.Unit/Features/FeatureStateServiceTests.cs

@@ -43,7 +43,7 @@ public class FeatureStateServiceTests
         _db.SetupDbSetWithGeneratedIds(c => c.FeatureStates, _featureStates);
 
         var webhookQueue = new WebhookQueue();
-        var auditService = new Mock<AuditService>(_db.Object, null!, webhookQueue);
+        var auditService = new Mock<IAuditService>();
         auditService.Setup(a => a.RecordAsync(
             It.IsAny<string>(), It.IsAny<string>(), It.IsAny<string>(),
             It.IsAny<int>(), It.IsAny<int?>(), It.IsAny<int?>(),
@@ -154,7 +154,7 @@ public class FeatureStateServiceTests
         var state = AddState();
         var queue = new WebhookQueue();
 
-        var auditService = new Mock<AuditService>(_db.Object, null!, queue);
+        var auditService = new Mock<IAuditService>();
         auditService.Setup(a => a.RecordAsync(
             It.IsAny<string>(), It.IsAny<string>(), It.IsAny<string>(),
             It.IsAny<int>(), It.IsAny<int?>(), It.IsAny<int?>(),

tests/api/MicCheck.Api.Tests.Unit/Features/FeaturesControllerTests.cs

@@ -41,7 +41,7 @@ public class FeaturesControllerTests
         _db.SetupDbSetWithGeneratedIds(c => c.Tags, _tags);
 
         var webhookQueue = new MicCheck.Api.Webhooks.WebhookQueue();
-        var auditService = new Mock<AuditService>(_db.Object, null!, webhookQueue);
+        var auditService = new Mock<IAuditService>();
         auditService.Setup(a => a.RecordAsync(
             It.IsAny<string>(), It.IsAny<string>(), It.IsAny<string>(),
             It.IsAny<int>(), It.IsAny<int?>(), It.IsAny<int?>(),

tests/api/MicCheck.Api.Tests.Unit/Features/FlagsApiIntegrationTests.cs

@@ -2,6 +2,7 @@ using System.Security.Claims;
 using MicCheck.Api.Data;
 using MicCheck.Api.Environments;
 using MicCheck.Api.Features;
+using MicCheck.Api.Features.Usage;
 using MicCheck.Api.Identities;
 using MicCheck.Api.Projects;
 using MicCheck.Api.Segments;

tests/api/MicCheck.Api.Tests.Unit/Features/Usage/FeatureUsageControllerTests.cs

@@ -1,12 +1,12 @@
 using MicCheck.Api.Data;
-using MicCheck.Api.Features;
+using MicCheck.Api.Features.Usage;
 using MicCheck.Api.Tests.Unit.TestSupport;
 using Microsoft.AspNetCore.Mvc;
 using Microsoft.Extensions.Caching.Memory;
 using Moq;
 using NUnit.Framework;
 
-namespace MicCheck.Api.Tests.Unit.Features;
+namespace MicCheck.Api.Tests.Unit.Features.Usage;
 
 [TestFixture]
 public class FeatureUsageControllerTests

tests/api/MicCheck.Api.Tests.Unit/Features/Usage/FeatureUsageMetricsTests.cs

@@ -1,9 +1,9 @@
 using System.Diagnostics.Metrics;
-using MicCheck.Api.Features;
+using MicCheck.Api.Features.Usage;
 using Moq;
 using NUnit.Framework;
 
-namespace MicCheck.Api.Tests.Unit.Features;
+namespace MicCheck.Api.Tests.Unit.Features.Usage;
 
 [TestFixture]
 public class FeatureUsageMetricsTests

tests/api/MicCheck.Api.Tests.Unit/Features/Usage/FeatureUsageQueryServiceTests.cs

@@ -1,10 +1,10 @@
 using MicCheck.Api.Data;
-using MicCheck.Api.Features;
+using MicCheck.Api.Features.Usage;
 using MicCheck.Api.Tests.Unit.TestSupport;
 using Moq;
 using NUnit.Framework;
 
-namespace MicCheck.Api.Tests.Unit.Features;
+namespace MicCheck.Api.Tests.Unit.Features.Usage;
 
 [TestFixture]
 public class FeatureUsageQueryServiceTests

tests/api/MicCheck.Api.Tests.Unit/Identities/IdentitiesControllerTests.cs

@@ -2,6 +2,7 @@ using System.Security.Claims;
 using MicCheck.Api.Data;
 using MicCheck.Api.Environments;
 using MicCheck.Api.Features;
+using MicCheck.Api.Features.Usage;
 using MicCheck.Api.Identities;
 using MicCheck.Api.Projects;
 using MicCheck.Api.Segments;

tests/api/MicCheck.Api.Tests.Unit/Organizations/OrganizationServiceTests.cs

@@ -41,7 +41,7 @@ public class OrganizationServiceTests
         _db.SetupDbSet(c => c.Users, _users);
 
         var webhookQueue = new MicCheck.Api.Webhooks.WebhookQueue();
-        var auditService = new Mock<AuditService>(_db.Object, null!, webhookQueue);
+        var auditService = new Mock<IAuditService>();
         auditService.Setup(a => a.LogAsync(
             It.IsAny<string>(), It.IsAny<string>(), It.IsAny<string>(),
             It.IsAny<int>(), It.IsAny<int?>(), It.IsAny<int?>(),

tests/api/MicCheck.Api.Tests.Unit/Organizations/OrganizationsControllerTests.cs

@@ -49,7 +49,7 @@ public class OrganizationsControllerTests
         _db.SetupDbSetWithGeneratedIds(c => c.Webhooks, _webhooks);
 
         var webhookQueue = new WebhookQueue();
-        var auditService = new Mock<AuditService>(_db.Object, null!, webhookQueue);
+        var auditService = new Mock<IAuditService>();
         auditService.Setup(a => a.LogAsync(
             It.IsAny<string>(), It.IsAny<string>(), It.IsAny<string>(),
             It.IsAny<int>(), It.IsAny<int?>(), It.IsAny<int?>(),

tests/api/MicCheck.Api.Tests.Unit/Projects/ProjectServiceTests.cs

@@ -32,7 +32,7 @@ public class ProjectServiceTests
         _db.SetupDbSet(c => c.UserProjectPermissions, _permissions);
 
         var webhookQueue = new MicCheck.Api.Webhooks.WebhookQueue();
-        var auditService = new Mock<AuditService>(_db.Object, null!, webhookQueue);
+        var auditService = new Mock<IAuditService>();
         auditService.Setup(a => a.LogAsync(
             It.IsAny<string>(), It.IsAny<string>(), It.IsAny<string>(),
             It.IsAny<int>(), It.IsAny<int?>(), It.IsAny<int?>(),

tests/api/MicCheck.Api.Tests.Unit/Projects/ProjectsControllerTests.cs

@@ -34,7 +34,7 @@ public class ProjectsControllerTests
         _db.SetupDbSet(c => c.UserProjectPermissions, _permissions);
 
         var webhookQueue = new MicCheck.Api.Webhooks.WebhookQueue();
-        var auditService = new Mock<AuditService>(_db.Object, null!, webhookQueue);
+        var auditService = new Mock<IAuditService>();
         auditService.Setup(a => a.LogAsync(
             It.IsAny<string>(), It.IsAny<string>(), It.IsAny<string>(),
             It.IsAny<int>(), It.IsAny<int?>(), It.IsAny<int?>(),

tests/api/MicCheck.Api.Tests.Unit/Segments/SegmentServiceTests.cs

@@ -40,7 +40,7 @@ public class SegmentServiceTests
         _db.SetupDbSetWithGeneratedIds(c => c.SegmentConditions, _segmentConditions);
 
         var webhookQueue = new MicCheck.Api.Webhooks.WebhookQueue();
-        var auditService = new Mock<AuditService>(_db.Object, null!, webhookQueue);
+        var auditService = new Mock<IAuditService>();
         auditService.Setup(a => a.LogAsync(
             It.IsAny<string>(), It.IsAny<string>(), It.IsAny<string>(),
             It.IsAny<int>(), It.IsAny<int?>(), It.IsAny<int?>(),

tests/api/MicCheck.Api.Tests.Unit/Segments/SegmentsControllerTests.cs

@@ -41,7 +41,7 @@ public class SegmentsControllerTests
         _db.SetupDbSetWithGeneratedIds(c => c.SegmentConditions, _segmentConditions);
 
         var webhookQueue = new MicCheck.Api.Webhooks.WebhookQueue();
-        var auditService = new Mock<AuditService>(_db.Object, null!, webhookQueue);
+        var auditService = new Mock<IAuditService>();
         auditService.Setup(a => a.LogAsync(
             It.IsAny<string>(), It.IsAny<string>(), It.IsAny<string>(),
             It.IsAny<int>(), It.IsAny<int?>(), It.IsAny<int?>(),