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>

src/KArtSell.Host/Jobs/OpenDartDailyBatchJob.cs

@@ -1,5 +1,6 @@
 using Dapper;
 using Hangfire;
+using KArtSell.BuildingBlocks.Time;
 using KArtSell.Host.Observability;
 using Microsoft.Extensions.Logging;
 using Npgsql;
@@ -15,6 +16,7 @@ public class OpenDartDailyBatchJob
 {
     private readonly OpenDartService _openDart;
     private readonly NpgsqlDataSource _dataSource;
+    private readonly IClock _clock;
     private readonly ILogger<OpenDartDailyBatchJob> _logger;
 
     private static readonly Action<ILogger, int, int, Exception?> LogBatchStart =
@@ -32,16 +34,18 @@ public class OpenDartDailyBatchJob
     public OpenDartDailyBatchJob(
         OpenDartService openDart,
         NpgsqlDataSource dataSource,
+        IClock clock,
         ILogger<OpenDartDailyBatchJob> logger)
     {
         _openDart = openDart;
         _dataSource = dataSource;
+        _clock = clock;
         _logger = logger;
     }
 
     public async Task ExecuteAsync(CancellationToken cancellationToken = default)
     {
-        var batchDate = DateOnly.FromDateTime(DateTime.UtcNow);
+        var batchDate = DateOnly.FromDateTime(_clock.UtcNow.UtcDateTime);
         var quotaLimit = 1000;
 
         // 1. Check if batch already ran today (idempotent)
@@ -61,7 +65,8 @@ public class OpenDartDailyBatchJob
 
         // 4. Fetch latest quarterly data for each ticker
         var successCount = 0;
-        var currentQuarter = GetCurrentQuarter();
+        var quarter = (int)(_clock.UtcNow.UtcDateTime.Month - 1) / 3 + 1;
+        var currentQuarter = $"{_clock.UtcNow.UtcDateTime.Year}-Q{quarter}";
 
         foreach (var ticker in tickers)
         {
@@ -100,7 +105,7 @@ public class OpenDartDailyBatchJob
         await using var connection = await _dataSource.OpenConnectionAsync(cancellationToken);
         var tickers = await connection.QueryAsync<string>(
             sql,
-            new { now = DateTime.UtcNow },
+            new { now = _clock.UtcNow.UtcDateTime },
             commandTimeout: 5);
 
         return tickers.ToList();
@@ -161,10 +166,4 @@ public class OpenDartDailyBatchJob
             commandTimeout: 5);
     }
 
-    private static string GetCurrentQuarter()
-    {
-        var now = DateTime.UtcNow;
-        var quarter = (now.Month - 1) / 3 + 1;
-        return $"{now.Year}-Q{quarter}";
-    }
 }