feat: sam_stat P2 도메인 + 통계 API + 대시보드 전환 (Phase 4)

- 4.1: stat_project_monthly + ProjectStatService (건설/프로젝트 월간)
- 4.2: stat_system_daily + SystemStatService (API/감사/FCM/파일/결재)
- 4.3: stat_events, stat_snapshots + StatEventService + StatEventObserver
- 4.4: StatController (summary/daily/monthly/alerts) + StatQueryService + FormRequest 3개 + routes/stats.php
- 4.5: DashboardService sam_stat 우선 조회 + 원본 DB 폴백 패턴

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

app/Services/Stats/StatEventService.php

@@ -0,0 +1,74 @@
+<?php
+
+namespace App\Services\Stats;
+
+use App\Models\Stats\StatEvent;
+use App\Models\Stats\StatSnapshot;
+use Illuminate\Support\Facades\Log;
+
+class StatEventService
+{
+    /**
+     * 통계 이벤트 기록
+     */
+    public function recordEvent(
+        int $tenantId,
+        string $domain,
+        string $eventType,
+        string $entityType,
+        int $entityId,
+        ?array $payload = null
+    ): void {
+        try {
+            StatEvent::create([
+                'tenant_id' => $tenantId,
+                'domain' => $domain,
+                'event_type' => $eventType,
+                'entity_type' => $entityType,
+                'entity_id' => $entityId,
+                'payload' => $payload,
+                'occurred_at' => now(),
+            ]);
+        } catch (\Throwable $e) {
+            Log::warning('stat_event 기록 실패', [
+                'tenant_id' => $tenantId,
+                'domain' => $domain,
+                'event_type' => $eventType,
+                'error' => $e->getMessage(),
+            ]);
+        }
+    }
+
+    /**
+     * 스냅샷 저장
+     */
+    public function saveSnapshot(
+        int $tenantId,
+        string $domain,
+        string $snapshotDate,
+        array $data,
+        string $snapshotType = 'daily'
+    ): void {
+        try {
+            StatSnapshot::updateOrCreate(
+                [
+                    'tenant_id' => $tenantId,
+                    'snapshot_date' => $snapshotDate,
+                    'domain' => $domain,
+                    'snapshot_type' => $snapshotType,
+                ],
+                [
+                    'data' => $data,
+                    'created_at' => now(),
+                ]
+            );
+        } catch (\Throwable $e) {
+            Log::warning('stat_snapshot 저장 실패', [
+                'tenant_id' => $tenantId,
+                'domain' => $domain,
+                'snapshot_date' => $snapshotDate,
+                'error' => $e->getMessage(),
+            ]);
+        }
+    }
+}