feat: enhance usage analytics dashboard (#666)

- visualize input, output, and cache token segments in usage charts
- add usage period selector for 7d, 30d, 90d, and 365d
- guard usage stats against stale overlapping period requests
- normalize blank model usage into unknown buckets
- add client and server coverage for usage analytics behavior

packages/client/src/i18n/locales/zh.ts

@@ -975,7 +975,7 @@ export default {
     estimatedCost: '预估费用',
     cacheHitRate: '缓存命中率',
     modelBreakdown: '模型分布',
-    dailyTrend: '每日用量（近 30 天）',
+    dailyTrend: '每日用量',
     date: '日期',
     tokens: 'Token',
     cache: '缓存',