feat: DB 백업 시스템 구축 (Phase 1,2,4)

- Phase 1: backup.conf.example + sam-db-backup.sh 백업 스크립트
- Phase 2: BackupCheckCommand + StatMonitorService.recordBackupFailure()
- Phase 2: routes/console.php에 db:backup-check 05:00 스케줄 등록
- Phase 4: SlackNotificationService 생성 (웹훅 알림)
- Phase 4: BackupCheckCommand/StatMonitorService에 Slack 알림 연동

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

app/Services/Stats/StatMonitorService.php

@@ -3,6 +3,7 @@
 namespace App\Services\Stats;
 
 use App\Models\Stats\StatAlert;
+use App\Services\SlackNotificationService;
 use Illuminate\Support\Facades\Log;
 
 class StatMonitorService
@@ -26,6 +27,13 @@ public function recordAggregationFailure(int $tenantId, string $domain, string $
                 'is_resolved' => false,
                 'created_at' => now(),
             ]);
+
+            // critical 알림 Slack 전송
+            app(SlackNotificationService::class)->sendStatAlert(
+                "[{$jobType}] 집계 실패",
+                mb_substr($errorMessage, 0, 300),
+                $domain
+            );
         } catch (\Throwable $e) {
             Log::error('stat_alert 기록 실패', [
                 'tenant_id' => $tenantId,
@@ -94,6 +102,13 @@ public function recordMismatch(int $tenantId, string $domain, string $label, flo
                 'is_resolved' => false,
                 'created_at' => now(),
             ]);
+
+            // critical 알림 Slack 전송
+            app(SlackNotificationService::class)->sendStatAlert(
+                "[{$label}] 정합성 불일치",
+                "원본={$expected}, 통계={$actual}, 차이=" . ($actual - $expected),
+                $domain
+            );
         } catch (\Throwable $e) {
             Log::error('stat_alert 기록 실패 (mismatch)', [
                 'tenant_id' => $tenantId,
@@ -103,6 +118,33 @@ public function recordMismatch(int $tenantId, string $domain, string $label, flo
         }
     }
 
+    /**
+     * 백업 실패 알림 기록 (시스템 레벨, tenantId=0)
+     */
+    public function recordBackupFailure(string $title, string $message): void
+    {
+        try {
+            StatAlert::create([
+                'tenant_id' => 0,
+                'alert_type' => 'backup_failure',
+                'domain' => 'backup',
+                'severity' => 'critical',
+                'title' => $title,
+                'message' => mb_substr($message, 0, 500),
+                'current_value' => 0,
+                'threshold_value' => 0,
+                'is_read' => false,
+                'is_resolved' => false,
+                'created_at' => now(),
+            ]);
+        } catch (\Throwable $e) {
+            Log::error('stat_alert 기록 실패 (backup_failure)', [
+                'title' => $title,
+                'error' => $e->getMessage(),
+            ]);
+        }
+    }
+
     /**
      * 알림 해결 처리
      */