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/ProjectStatService.php

@@ -0,0 +1,92 @@
+<?php
+
+namespace App\Services\Stats;
+
+use App\Models\Stats\Monthly\StatProjectMonthly;
+use Carbon\Carbon;
+use Illuminate\Support\Facades\DB;
+
+class ProjectStatService implements StatDomainServiceInterface
+{
+    public function aggregateDaily(int $tenantId, Carbon $date): int
+    {
+        // 건설/프로젝트는 월간 전용 (일간 집계 없음)
+        return 0;
+    }
+
+    public function aggregateMonthly(int $tenantId, int $year, int $month): int
+    {
+        $startDate = Carbon::create($year, $month, 1)->startOfDay();
+        $endDate = $startDate->copy()->endOfMonth();
+
+        // 현장 현황
+        $activeSites = DB::connection('mysql')
+            ->table('sites')
+            ->where('tenant_id', $tenantId)
+            ->where('status', 'active')
+            ->whereNull('deleted_at')
+            ->count();
+
+        $completedSites = DB::connection('mysql')
+            ->table('sites')
+            ->where('tenant_id', $tenantId)
+            ->where('status', 'completed')
+            ->whereNull('deleted_at')
+            ->count();
+
+        // 계약 현황 (해당 월 신규 계약)
+        $contractStats = DB::connection('mysql')
+            ->table('contracts')
+            ->where('tenant_id', $tenantId)
+            ->whereBetween('created_at', [$startDate, $endDate])
+            ->whereNull('deleted_at')
+            ->selectRaw('
+                COUNT(*) as new_count,
+                COALESCE(SUM(contract_amount), 0) as total_amount
+            ')
+            ->first();
+
+        // 지출예상 (해당 월)
+        $expenseStats = DB::connection('mysql')
+            ->table('expected_expenses')
+            ->where('tenant_id', $tenantId)
+            ->whereYear('expected_payment_date', $year)
+            ->whereMonth('expected_payment_date', $month)
+            ->whereNull('deleted_at')
+            ->selectRaw('
+                COALESCE(SUM(amount), 0) as expected_total,
+                COALESCE(SUM(CASE WHEN payment_status = \'paid\' THEN amount ELSE 0 END), 0) as actual_total
+            ')
+            ->first();
+
+        // 수익률 계산
+        $contractTotal = (float) ($contractStats->total_amount ?? 0);
+        $actualExpense = (float) ($expenseStats->actual_total ?? 0);
+        $grossProfit = $contractTotal - $actualExpense;
+        $grossProfitRate = $contractTotal > 0 ? ($grossProfit / $contractTotal) * 100 : 0;
+
+        StatProjectMonthly::updateOrCreate(
+            [
+                'tenant_id' => $tenantId,
+                'stat_year' => $year,
+                'stat_month' => $month,
+            ],
+            [
+                'active_site_count' => $activeSites,
+                'completed_site_count' => $completedSites,
+                'new_contract_count' => $contractStats->new_count ?? 0,
+                'contract_total_amount' => $contractTotal,
+                'expected_expense_total' => $expenseStats->expected_total ?? 0,
+                'actual_expense_total' => $actualExpense,
+                'labor_cost_total' => 0,
+                'material_cost_total' => 0,
+                'gross_profit' => $grossProfit,
+                'gross_profit_rate' => $grossProfitRate,
+                'handover_report_count' => 0,
+                'structure_review_count' => 0,
+            ]
+        );
+
+        return 1;
+    }
+}