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/SlackNotificationService.php

@@ -0,0 +1,136 @@
+<?php
+
+namespace App\Services;
+
+use Illuminate\Support\Facades\Http;
+use Illuminate\Support\Facades\Log;
+
+class SlackNotificationService
+{
+    private ?string $webhookUrl;
+
+    private string $serverName;
+
+    private bool $enabled;
+
+    public function __construct()
+    {
+        $this->webhookUrl = env('SLACK_ALERT_WEBHOOK_URL') ?: env('LOG_SLACK_WEBHOOK_URL');
+        $this->serverName = env('SLACK_ALERT_SERVER_NAME', config('app.env', 'unknown'));
+        $this->enabled = (bool) env('SLACK_ALERT_ENABLED', false);
+    }
+
+    /**
+     * 일반 알림 전송
+     */
+    public function sendAlert(string $title, string $message, string $severity = 'critical'): void
+    {
+        $color = match ($severity) {
+            'critical' => '#FF0000',
+            'warning' => '#FFA500',
+            default => '#3498DB',
+        };
+
+        $emoji = match ($severity) {
+            'critical' => ':rotating_light:',
+            'warning' => ':warning:',
+            default => ':information_source:',
+        };
+
+        $this->send([
+            'attachments' => [
+                [
+                    'color' => $color,
+                    'blocks' => [
+                        [
+                            'type' => 'header',
+                            'text' => [
+                                'type' => 'plain_text',
+                                'text' => "{$emoji} {$title}",
+                                'emoji' => true,
+                            ],
+                        ],
+                        [
+                            'type' => 'section',
+                            'fields' => [
+                                [
+                                    'type' => 'mrkdwn',
+                                    'text' => "*서버:*\n{$this->serverName}",
+                                ],
+                                [
+                                    'type' => 'mrkdwn',
+                                    'text' => '*시간:*\n' . now()->format('Y-m-d H:i:s'),
+                                ],
+                            ],
+                        ],
+                        [
+                            'type' => 'section',
+                            'text' => [
+                                'type' => 'mrkdwn',
+                                'text' => "*상세:*\n{$message}",
+                            ],
+                        ],
+                        [
+                            'type' => 'context',
+                            'elements' => [
+                                [
+                                    'type' => 'mrkdwn',
+                                    'text' => "환경: `" . config('app.env') . "` | 심각도: `{$severity}`",
+                                ],
+                            ],
+                        ],
+                    ],
+                ],
+            ],
+        ]);
+    }
+
+    /**
+     * 백업 실패 알림
+     */
+    public function sendBackupAlert(string $title, string $message): void
+    {
+        $this->sendAlert("[SAM 백업 실패] {$title}", $message, 'critical');
+    }
+
+    /**
+     * 통계/모니터링 알림
+     */
+    public function sendStatAlert(string $title, string $message, string $domain): void
+    {
+        $this->sendAlert("[SAM {$domain}] {$title}", $message, 'critical');
+    }
+
+    /**
+     * Slack 웹훅으로 메시지 전송
+     */
+    private function send(array $payload): void
+    {
+        if (! $this->enabled) {
+            Log::debug('Slack 알림 비활성화 상태 (SLACK_ALERT_ENABLED=false)');
+
+            return;
+        }
+
+        if (empty($this->webhookUrl)) {
+            Log::warning('Slack 웹훅 URL 미설정');
+
+            return;
+        }
+
+        try {
+            $response = Http::timeout(10)->post($this->webhookUrl, $payload);
+
+            if (! $response->successful()) {
+                Log::error('Slack 알림 전송 실패', [
+                    'status' => $response->status(),
+                    'body' => $response->body(),
+                ]);
+            }
+        } catch (\Throwable $e) {
+            Log::error('Slack 알림 전송 예외', [
+                'error' => $e->getMessage(),
+            ]);
+        }
+    }
+}