feat: [settings] AI 토큰사용량 조회 API 추가

- GET /settings/ai-token-usage: 목록 + 통계 조회
- GET /settings/ai-token-usage/pricing: 단가 설정 조회 (읽기 전용)
- AiTokenHelper: Gemini/Claude/R2/STT 사용량 기록 헬퍼
- AiPricingConfig 캐시에 cloudflare-r2 provider 추가

app/Services/AiTokenUsageService.php

@@ -0,0 +1,72 @@
+<?php
+
+namespace App\Services;
+
+use App\Models\Tenants\AiPricingConfig;
+use App\Models\Tenants\AiTokenUsage;
+
+class AiTokenUsageService extends Service
+{
+    /**
+     * 토큰 사용량 목록 + 통계
+     */
+    public function list(array $params): array
+    {
+        $tenantId = $this->tenantId();
+
+        $query = AiTokenUsage::where('tenant_id', $tenantId)
+            ->when($params['start_date'] ?? null, fn ($q, $d) => $q->whereDate('created_at', '>=', $d))
+            ->when($params['end_date'] ?? null, fn ($q, $d) => $q->whereDate('created_at', '<=', $d))
+            ->when($params['menu_name'] ?? null, fn ($q, $m) => $q->where('menu_name', $m));
+
+        // 통계 (페이지네이션 전 전체 집계)
+        $stats = (clone $query)->selectRaw('
+            COUNT(*) as total_count,
+            COALESCE(SUM(prompt_tokens), 0) as total_prompt_tokens,
+            COALESCE(SUM(completion_tokens), 0) as total_completion_tokens,
+            COALESCE(SUM(total_tokens), 0) as total_total_tokens,
+            COALESCE(SUM(cost_usd), 0) as total_cost_usd,
+            COALESCE(SUM(cost_krw), 0) as total_cost_krw
+        ')->first();
+
+        // 목록 (페이지네이션)
+        $items = $query->with('creator:id,name')
+            ->orderByDesc('created_at')
+            ->paginate($params['per_page'] ?? 20);
+
+        // 메뉴명 필터 옵션
+        $menuNames = AiTokenUsage::where('tenant_id', $tenantId)
+            ->select('menu_name')
+            ->distinct()
+            ->orderBy('menu_name')
+            ->pluck('menu_name');
+
+        return [
+            'items' => $items,
+            'stats' => [
+                'total_count' => (int) $stats->total_count,
+                'total_prompt_tokens' => (int) $stats->total_prompt_tokens,
+                'total_completion_tokens' => (int) $stats->total_completion_tokens,
+                'total_total_tokens' => (int) $stats->total_total_tokens,
+                'total_cost_usd' => (float) $stats->total_cost_usd,
+                'total_cost_krw' => (float) $stats->total_cost_krw,
+            ],
+            'menu_names' => $menuNames,
+        ];
+    }
+
+    /**
+     * 단가 설정 조회 (읽기 전용)
+     */
+    public function getPricing(): array
+    {
+        $configs = AiPricingConfig::where('is_active', true)
+            ->orderBy('provider')
+            ->get();
+
+        return [
+            'pricing' => $configs,
+            'exchange_rate' => AiPricingConfig::getExchangeRate(),
+        ];
+    }
+}