fix: Replace all DateTime.Now/UtcNow with IClock injection (AGENTS.md v16.0)

Resolves architecture test violations:
- Removed all direct DateTime.UtcNow calls
- Injected IClock into 7 service classes
- Added TestClock implementation for tests
- Updated all test constructors with fixture.Clock()
- Fixed MetricsSql comment to avoid false SELECT * detection

Services updated (IClock injection):
- MetricsSql.cs (BuildingBlocks)
- CircuitBreakerPolicyFactory.cs
- KisConnectionPool.cs
- RateLimiterService.cs
- MetricsPolicy.cs
- OpenDartDailyBatchJob.cs
- OpenDartService.cs

Tests updated:
- DatabaseFixture.cs (added Clock() method + TestClock impl)
- CircuitBreakerTests, ObservabilityMetricsTests, OpenDartServiceTests, RateLimiterServiceTests (added fixture.Clock() to constructors)

Result: 95/95 integration tests PASS, DateTime violations 100% resolved

Co-Authored-By: Claude Haiku 4.5 <noreply@anthropic.com>

tests/KArtSell.Integration.Tests/CircuitBreakerTests.cs

@@ -14,7 +14,7 @@ public class CircuitBreakerTests : IAsyncLifetime
     public CircuitBreakerTests(DatabaseFixture fixture)
     {
         _dataSource = fixture.DataSource;
-        _factory = new CircuitBreakerPolicyFactory(_dataSource, fixture.Logger<CircuitBreakerPolicyFactory>());
+        _factory = new CircuitBreakerPolicyFactory(_dataSource, fixture.Clock(), fixture.Logger<CircuitBreakerPolicyFactory>());
     }
 
     public async Task InitializeAsync()

tests/KArtSell.Integration.Tests/DatabaseFixture.cs

@@ -1,4 +1,5 @@
 using Dapper;
+using KArtSell.BuildingBlocks.Time;
 using Microsoft.Extensions.Logging;
 using Npgsql;
 using System;
@@ -41,6 +42,16 @@ public class DatabaseFixture : IAsyncLifetime
     {
         return new XunitLogger<T>();
     }
+
+    public IClock Clock()
+    {
+        return new TestClock();
+    }
+}
+
+internal sealed class TestClock : IClock
+{
+    public DateTimeOffset UtcNow => DateTimeOffset.UtcNow;
 }
 
 internal sealed class XunitLogger<T> : ILogger<T>

tests/KArtSell.Integration.Tests/ObservabilityMetricsTests.cs

@@ -16,8 +16,8 @@ public class ObservabilityMetricsTests : IAsyncLifetime
     public ObservabilityMetricsTests(DatabaseFixture fixture)
     {
         _dataSource = fixture.DataSource;
-        _policy = new MetricsPolicy();
-        _sql = new MetricsSql(_dataSource);
+        _policy = new MetricsPolicy(fixture.Clock());
+        _sql = new MetricsSql(_dataSource, fixture.Clock());
     }
 
     public async Task InitializeAsync()

tests/KArtSell.Integration.Tests/OpenDartServiceTests.cs

@@ -17,7 +17,7 @@ public class OpenDartServiceTests : IAsyncLifetime
         // Set test API key to avoid initialization error
         if (string.IsNullOrEmpty(Environment.GetEnvironmentVariable("OPENDART_API_KEY")))
             Environment.SetEnvironmentVariable("OPENDART_API_KEY", "test-key-12345");
-        _service = new OpenDartService(_dataSource, new HttpClient(), fixture.Logger<OpenDartService>());
+        _service = new OpenDartService(_dataSource, new HttpClient(), fixture.Clock(), fixture.Logger<OpenDartService>());
     }
 
     public async Task InitializeAsync()

tests/KArtSell.Integration.Tests/RateLimiterServiceTests.cs

@@ -14,7 +14,7 @@ public class RateLimiterServiceTests : IAsyncLifetime
     public RateLimiterServiceTests(DatabaseFixture fixture)
     {
         _dataSource = fixture.DataSource;
-        _service = new RateLimiterService(_dataSource, fixture.Logger<RateLimiterService>());
+        _service = new RateLimiterService(_dataSource, fixture.Clock(), fixture.Logger<RateLimiterService>());
     }
 
     public async Task InitializeAsync()