refactor: extract common bandwidth formatting utilities

- Add BandwidthInfo interface to types.ts (single source of truth)
- Create formatters.ts with formatTB() and formatTrafficInfo()
- Display CDN hit rate and gross/origin traffic in recommendations
- Fix floating point formatting (consistent decimal places)
- Fix undefined handling in toLocaleString() calls
- Unify overage detection logic (overage_tb > 0 && cost > 0)
- Add CDN hit rate range validation (0-100%)
- Extract CDN_CACHE_HIT_RATES constants

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

src/tools/server-tool.ts

@@ -1,10 +1,20 @@
-import type { Env } from '../types';
+import type { Env, BandwidthInfo } from '../types';
 import { retryWithBackoff, RetryError } from '../utils/retry';
 import { createLogger, maskUserId } from '../utils/logger';
 import { ERROR_MESSAGES } from '../constants/messages';
+import { formatTrafficInfo } from '../utils/formatters';
 
 const logger = createLogger('server-tool');
 
+// CDN 캐시 히트율 상수
+const CDN_CACHE_HIT_RATES = {
+  VIDEO_STREAMING: 0.92,
+  STATIC_SITE: 0.95,
+  API: 0.30,
+  ECOMMERCE: 0.70,
+  DEFAULT: 0.85,
+} as const;
+
 // 언어 감지 (한글/일본어/중국어/영어)
 function detectLanguage(text: string): 'ko' | 'ja' | 'zh' | 'en' {
   if (/[가-힣]/.test(text)) return 'ko';
@@ -32,12 +42,12 @@ function estimateCdnCacheHitRate(techStack: string[], useCase: string): number |
   const isEcommerce = /shop|store|commerce|쇼핑|이커머스/.test(useCaseLower);
 
   // 콘텐츠 타입별 예상 캐시 히트율
-  if (isVideoStreaming) return 0.92;  // 비디오: 92% (대부분 캐시 가능)
-  if (isStaticSite) return 0.95;      // 정적 사이트: 95%
-  if (isApi) return 0.30;             // API: 30% (동적 콘텐츠 많음)
-  if (isEcommerce) return 0.70;       // 이커머스: 70% (상품 이미지 캐시)
+  if (isVideoStreaming) return CDN_CACHE_HIT_RATES.VIDEO_STREAMING;
+  if (isStaticSite) return CDN_CACHE_HIT_RATES.STATIC_SITE;
+  if (isApi) return CDN_CACHE_HIT_RATES.API;
+  if (isEcommerce) return CDN_CACHE_HIT_RATES.ECOMMERCE;
 
-  return 0.85;  // 기본값: 85%
+  return CDN_CACHE_HIT_RATES.DEFAULT;
 }
 
 // Type guards
@@ -94,16 +104,7 @@ interface ServerRecommendation {
     max_concurrent_users: number;
     requests_per_second: number;
   };
-  bandwidth_info?: {
-    included_transfer_tb: number;
-    overage_cost_per_gb: number;
-    overage_cost_per_tb: number;
-    estimated_monthly_tb: number;
-    estimated_overage_tb: number;
-    estimated_overage_cost: number;
-    total_estimated_cost: number;
-    currency: string;
-  };
+  bandwidth_info?: BandwidthInfo;
   benchmark_reference?: {
     processor_name: string;
     benchmarks: BenchmarkItem[];
@@ -334,20 +335,15 @@ function formatRecommendations(data: RecommendResponse): string {
 
     // 대역폭 정보 (항상 표시)
     if (rec.bandwidth_info) {
-      const bw = rec.bandwidth_info;
-      if (bw.estimated_overage_cost > 0) {
-        // 초과 비용 있음
-        const overageCost = bw.currency === 'KRW'
-          ? `₩${Math.round(bw.estimated_overage_cost).toLocaleString()}`
-          : `$${bw.estimated_overage_cost.toFixed(2)}`;
-        const totalCost = bw.currency === 'KRW'
-          ? `₩${Math.round(bw.total_estimated_cost).toLocaleString()}`
-          : `$${bw.total_estimated_cost.toFixed(2)}`;
-        response += `   • 예상 트래픽: ${bw.estimated_monthly_tb}TB → 초과 ${bw.estimated_overage_tb}TB (${overageCost})\n`;
+      const trafficInfo = formatTrafficInfo(rec.bandwidth_info, server.currency);
+      response += `   • ${trafficInfo}\n`;
+
+      // 총 예상 비용 (초과 있을 때만 표시)
+      if (rec.bandwidth_info.estimated_overage_tb > 0 && rec.bandwidth_info.estimated_overage_cost > 0) {
+        const totalCost = server.currency === 'KRW'
+          ? `₩${Math.round(rec.bandwidth_info.total_estimated_cost).toLocaleString()}`
+          : `$${rec.bandwidth_info.total_estimated_cost.toFixed(2)}`;
         response += `   • 총 예상 비용: ${totalCost}/월\n`;
-      } else {
-        // 포함 범위 내
-        response += `   • 예상 트래픽: ${bw.estimated_monthly_tb}TB (포함 범위 내)\n`;
       }
     }