feat: DataRetentionWorker 구현 (#152)

- 매일 04:00 KST 스케줄 실행
- PushSendLog/PushOpenLog: 90일 보관, WebhookLog: 30일, SystemLog: 180일
- 배치 단위 10000건씩 삭제 (트랜잭션 없음)
- SystemLog에 정리 완료 로그 기록
- DI에 AddHostedService 등록

Closes #152

SPMS.Infrastructure/DependencyInjection.cs

@@ -84,6 +84,7 @@ public static class DependencyInjection
         services.AddHostedService<ScheduleWorker>();
         services.AddHostedService<DailyStatWorker>();
         services.AddHostedService<DeadTokenCleanupWorker>();
+        services.AddHostedService<DataRetentionWorker>();
 
         // Token Store & Email Service
         services.AddMemoryCache();

SPMS.Infrastructure/Workers/DataRetentionWorker.cs

@@ -0,0 +1,124 @@
+using Microsoft.EntityFrameworkCore;
+using Microsoft.Extensions.DependencyInjection;
+using Microsoft.Extensions.Hosting;
+using Microsoft.Extensions.Logging;
+using SPMS.Domain.Entities;
+using SPMS.Infrastructure.Persistence;
+
+namespace SPMS.Infrastructure.Workers;
+
+public class DataRetentionWorker : BackgroundService
+{
+    private readonly IServiceScopeFactory _scopeFactory;
+    private readonly ILogger<DataRetentionWorker> _logger;
+
+    private static readonly TimeZoneInfo KstZone = TimeZoneInfo.FindSystemTimeZoneById("Asia/Seoul");
+    private const int BatchSize = 10000;
+
+    private static readonly (string TableName, string DateColumn, int RetentionDays)[] RetentionPolicies =
+    {
+        ("PushSendLog", "SentAt", 90),
+        ("PushOpenLog", "OpenedAt", 90),
+        ("WebhookLog", "SentAt", 30),
+        ("SystemLog", "CreatedAt", 180)
+    };
+
+    public DataRetentionWorker(
+        IServiceScopeFactory scopeFactory,
+        ILogger<DataRetentionWorker> logger)
+    {
+        _scopeFactory = scopeFactory;
+        _logger = logger;
+    }
+
+    protected override async Task ExecuteAsync(CancellationToken stoppingToken)
+    {
+        _logger.LogInformation("DataRetentionWorker 시작");
+
+        while (!stoppingToken.IsCancellationRequested)
+        {
+            var delay = CalculateDelayUntilNextRun();
+            _logger.LogInformation("DataRetentionWorker 다음 실행까지 {Delay} 대기", delay);
+
+            try
+            {
+                await Task.Delay(delay, stoppingToken);
+            }
+            catch (TaskCanceledException)
+            {
+                break;
+            }
+
+            try
+            {
+                await PurgeAsync(stoppingToken);
+            }
+            catch (Exception ex)
+            {
+                _logger.LogError(ex, "DataRetentionWorker 정리 중 오류 발생");
+            }
+        }
+    }
+
+    private TimeSpan CalculateDelayUntilNextRun()
+    {
+        var nowKst = TimeZoneInfo.ConvertTimeFromUtc(DateTime.UtcNow, KstZone);
+        var nextRun = nowKst.Date.AddHours(4);
+
+        if (nowKst >= nextRun)
+            nextRun = nextRun.AddDays(1);
+
+        return nextRun - nowKst;
+    }
+
+    private async Task PurgeAsync(CancellationToken stoppingToken)
+    {
+        using var scope = _scopeFactory.CreateScope();
+        var context = scope.ServiceProvider.GetRequiredService<AppDbContext>();
+
+        _logger.LogInformation("DataRetentionWorker 정리 시작");
+
+        var totalDeletedAll = 0;
+
+        foreach (var (tableName, dateColumn, retentionDays) in RetentionPolicies)
+        {
+            if (stoppingToken.IsCancellationRequested) break;
+
+            var cutoffUtc = DateTime.UtcNow.AddDays(-retentionDays);
+            var totalDeleted = 0;
+            int deletedInBatch;
+
+            do
+            {
+                var sql = $"DELETE FROM `{tableName}` WHERE `{dateColumn}` < @p0 LIMIT {BatchSize}";
+                deletedInBatch = await context.Database
+                    .ExecuteSqlRawAsync(sql, new[] { cutoffUtc }, stoppingToken);
+
+                totalDeleted += deletedInBatch;
+
+                if (deletedInBatch > 0)
+                    _logger.LogInformation(
+                        "DataRetentionWorker [{Table}] 배치 삭제: {BatchCount}건 (누적: {TotalDeleted}건)",
+                        tableName, deletedInBatch, totalDeleted);
+            } while (deletedInBatch > 0 && !stoppingToken.IsCancellationRequested);
+
+            if (totalDeleted > 0)
+                _logger.LogInformation(
+                    "DataRetentionWorker [{Table}] 정리 완료: {TotalDeleted}건 삭제 (보관 기간: {Days}일)",
+                    tableName, totalDeleted, retentionDays);
+
+            totalDeletedAll += totalDeleted;
+        }
+
+        // SystemLog에 정리 완료 기록
+        context.Set<SystemLog>().Add(new SystemLog
+        {
+            Action = "DataRetention",
+            Details = $"데이터 보관 주기 정리 완료: 총 {totalDeletedAll}건 삭제",
+            CreatedAt = DateTime.UtcNow
+        });
+        await context.SaveChangesAsync(stoppingToken);
+
+        _logger.LogInformation("DataRetentionWorker 전체 정리 완료: 총 {TotalDeleted}건 삭제", totalDeletedAll);
+    }
+}