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/Http/Requests/V1/AiTokenUsageListRequest.php

@@ -0,0 +1,24 @@
+<?php
+
+namespace App\Http\Requests\V1;
+
+use Illuminate\Foundation\Http\FormRequest;
+
+class AiTokenUsageListRequest extends FormRequest
+{
+    public function authorize(): bool
+    {
+        return true;
+    }
+
+    public function rules(): array
+    {
+        return [
+            'start_date' => 'nullable|date',
+            'end_date' => 'nullable|date|after_or_equal:start_date',
+            'menu_name' => 'nullable|string|max:100',
+            'per_page' => 'nullable|integer|min:10|max:100',
+            'page' => 'nullable|integer|min:1',
+        ];
+    }
+}