refactor(rust): 拆分 usage sql 仓储为模块并外置 SQL 文件

- 将 usage/sql.rs 拆分为 sql/mod.rs 与 sql/tests.rs
- 将内联 SQL 抽离到 sql/queries/ 目录下的独立 .sql 文件
- 前端用量记录表格移除缓存创建 token 展示，保留 cache read 列

frontend/src/features/usage/components/UsageRecordsTable.vue

@@ -569,9 +569,9 @@
                 <span>{{ formatTokens(record.output_tokens || 0) }}</span>
               </div>
               <div class="flex items-center gap-1 text-muted-foreground">
-                <span :class="hasPositiveTokens(getRecordCacheCreationTokens(record)) ? 'text-foreground/70' : ''">{{ formatOptionalTokens(getRecordCacheCreationTokens(record)) }}</span>
-                <span>/</span>
                 <span :class="hasPositiveTokens(record.cache_read_input_tokens) ? 'text-foreground/70' : ''">{{ formatOptionalTokens(record.cache_read_input_tokens) }}</span>
+                <span>/</span>
+                <span>-</span>
               </div>
             </div>
           </TableCell>
@@ -689,7 +689,7 @@ import {
 import { RefreshCcw, Search } from 'lucide-vue-next'
 import { formatTokens, formatCurrency } from '@/utils/format'
 import { formatDateTime } from '../composables'
-import { getCacheCreationTokens, getEffectiveInputTokens } from '../token-normalization'
+import { getEffectiveInputTokens } from '../token-normalization'
 import {
   formatUsageStreamLabel,
   isUsageRecordFailed,
@@ -825,10 +825,6 @@ function getRecordEffectiveInputTokens(record: UsageRecord): number {
   return getEffectiveInputTokens(record)
 }
 
-function getRecordCacheCreationTokens(record: UsageRecord): number {
-  return getCacheCreationTokens(record)
-}
-
 function hasPositiveTokens(value: number | null | undefined): boolean {
   return typeof value === 'number' && Number.isFinite(value) && value > 0
 }