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/Http/Controllers/Api/V1/StatController.php

@@ -0,0 +1,64 @@
+<?php
+
+namespace App\Http\Controllers\Api\V1;
+
+use App\Helpers\ApiResponse;
+use App\Http\Controllers\Controller;
+use App\Http\Requests\V1\Stat\StatAlertRequest;
+use App\Http\Requests\V1\Stat\StatDailyRequest;
+use App\Http\Requests\V1\Stat\StatMonthlyRequest;
+use App\Services\Stats\StatQueryService;
+use Illuminate\Http\JsonResponse;
+
+class StatController extends Controller
+{
+    public function __construct(
+        private readonly StatQueryService $statQueryService
+    ) {}
+
+    /**
+     * 대시보드 요약 통계 (sam_stat 기반)
+     */
+    public function summary(): JsonResponse
+    {
+        $data = $this->statQueryService->getDashboardSummary();
+
+        return ApiResponse::handle(['data' => $data], __('message.fetched'));
+    }
+
+    /**
+     * 일간 통계 조회
+     */
+    public function daily(StatDailyRequest $request): JsonResponse
+    {
+        $data = $this->statQueryService->getDailyStat(
+            $request->validated('domain'),
+            $request->validated()
+        );
+
+        return ApiResponse::handle(['data' => $data], __('message.fetched'));
+    }
+
+    /**
+     * 월간 통계 조회
+     */
+    public function monthly(StatMonthlyRequest $request): JsonResponse
+    {
+        $data = $this->statQueryService->getMonthlyStat(
+            $request->validated('domain'),
+            $request->validated()
+        );
+
+        return ApiResponse::handle(['data' => $data], __('message.fetched'));
+    }
+
+    /**
+     * 알림 목록 조회
+     */
+    public function alerts(StatAlertRequest $request): JsonResponse
+    {
+        $data = $this->statQueryService->getAlerts($request->validated());
+
+        return ApiResponse::handle(['data' => $data], __('message.fetched'));
+    }
+}