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

src/api/MicCheck.Api/Audit/AuditLog.cs

@@ -1,6 +1,6 @@
 namespace MicCheck.Api.Audit;
 
-public class AuditLog
+public record AuditLog
 {
     public int Id { get; init; }
     public required string ResourceType { get; init; }

src/api/MicCheck.Api/Audit/AuditLogQueryService.cs

@@ -6,29 +6,25 @@ namespace MicCheck.Api.Audit;
 
 public class AuditLogQueryService(IMicCheckDbContext db)
 {
-    public async Task<PagedResult<AuditLogResponse>> ListByOrganizationAsync(
-        int organizationId, AuditLogFilter filter, CancellationToken ct = default)
+    public async Task<PagedResult<AuditLogResponse>> ListByOrganizationAsync(int organizationId, AuditLogFilter filter, CancellationToken ct = default)
     {
         var query = db.AuditLogs.Where(l => l.OrganizationId == organizationId);
         return await ApplyFilterAndPageAsync(query, filter, ct);
     }
 
-    public async Task<PagedResult<AuditLogResponse>> ListByProjectAsync(
-        int projectId, AuditLogFilter filter, CancellationToken ct = default)
+    public async Task<PagedResult<AuditLogResponse>> ListByProjectAsync(int projectId, AuditLogFilter filter, CancellationToken ct = default)
     {
         var query = db.AuditLogs.Where(l => l.ProjectId == projectId);
         return await ApplyFilterAndPageAsync(query, filter, ct);
     }
 
-    public async Task<PagedResult<AuditLogResponse>> ListByEnvironmentAsync(
-        int environmentId, AuditLogFilter filter, CancellationToken ct = default)
+    public async Task<PagedResult<AuditLogResponse>> ListByEnvironmentAsync(int environmentId, AuditLogFilter filter, CancellationToken ct = default)
     {
         var query = db.AuditLogs.Where(l => l.EnvironmentId == environmentId);
         return await ApplyFilterAndPageAsync(query, filter, ct);
     }
 
-    private async Task<PagedResult<AuditLogResponse>> ApplyFilterAndPageAsync(
-        IQueryable<AuditLog> query, AuditLogFilter filter, CancellationToken ct)
+    private async Task<PagedResult<AuditLogResponse>> ApplyFilterAndPageAsync(IQueryable<AuditLog> query, AuditLogFilter filter, CancellationToken ct)
     {
         if (filter.From.HasValue)
             query = query.Where(l => l.CreatedAt >= filter.From.Value);
@@ -66,4 +62,4 @@ public class AuditLogQueryService(IMicCheckDbContext db)
 
         return new PagedResult<AuditLogResponse>(total, items);
     }
-}
+}

src/api/MicCheck.Api/Audit/AuditService.cs

@@ -4,7 +4,7 @@ using MicCheck.Api.Webhooks;
 
 namespace MicCheck.Api.Audit;
 
-public class AuditService(IMicCheckDbContext db, IHttpContextAccessor httpContextAccessor, WebhookQueue webhookQueue)
+public class AuditService(IMicCheckDbContext db, IHttpContextAccessor httpContextAccessor, WebhookQueue webhookQueue) : IAuditService
 {
     private static readonly JsonSerializerOptions JsonOptions = new()
     {
@@ -12,7 +12,7 @@ public class AuditService(IMicCheckDbContext db, IHttpContextAccessor httpContex
         PropertyNamingPolicy = JsonNamingPolicy.CamelCase
     };
 
-    public virtual async Task RecordAsync(
+    public async Task RecordAsync(
         string resourceType,
         string resourceId,
         string action,
@@ -33,7 +33,7 @@ public class AuditService(IMicCheckDbContext db, IHttpContextAccessor httpContex
             }, JsonOptions);
         }
 
-        var actorUserId = ResolveActorUserId();
+        var actorUserId = GetCurrentUserId();
 
         var log = new AuditLog
         {
@@ -68,7 +68,7 @@ public class AuditService(IMicCheckDbContext db, IHttpContextAccessor httpContex
     }
 
     // Backward-compatible overload used by existing callers
-    public virtual async Task LogAsync(
+    public async Task LogAsync(
         string resourceType,
         string resourceId,
         string action,
@@ -78,7 +78,7 @@ public class AuditService(IMicCheckDbContext db, IHttpContextAccessor httpContex
         string? changes = null,
         CancellationToken ct = default)
     {
-        var actorUserId = ResolveActorUserId();
+        var actorUserId = GetCurrentUserId();
 
         var log = new AuditLog
         {
@@ -112,9 +112,33 @@ public class AuditService(IMicCheckDbContext db, IHttpContextAccessor httpContex
         });
     }
 
-    private int? ResolveActorUserId()
+    private int? GetCurrentUserId()
     {
         var claim = httpContextAccessor.HttpContext?.User.FindFirst(System.Security.Claims.ClaimTypes.NameIdentifier)?.Value;
         return int.TryParse(claim, out var id) ? id : null;
     }
 }
+
+public interface IAuditService
+{
+    Task RecordAsync(
+        string resourceType,
+        string resourceId,
+        string action,
+        int organizationId,
+        int? projectId = null,
+        int? environmentId = null,
+        object? before = null,
+        object? after = null,
+        CancellationToken ct = default);
+
+    Task LogAsync(
+        string resourceType,
+        string resourceId,
+        string action,
+        int organizationId,
+        int? projectId = null,
+        int? environmentId = null,
+        string? changes = null,
+        CancellationToken ct = default);
+}

src/api/MicCheck.Api/Audit/DependencyRegistration.cs

@@ -0,0 +1,12 @@
+namespace MicCheck.Api.Audit;
+
+public static class DependencyRegistration
+{
+    public static IServiceCollection AddAuditServices(this IServiceCollection services)
+    {
+        services.AddScoped<IAuditService, AuditService>();
+        services.AddScoped<AuditLogQueryService>();
+
+        return services;
+    }
+}