feat: 账号配额支持固定时间重置模式

- 后端新增 rolling/fixed 两种配额重置模式，支持日配额和周配额
- fixed 模式下可配置重置时刻（小时）、重置星期几（周配额）及时区（IANA）
- 在 account_repo.go 中使用 SQL 表达式适配两种模式的过期判断与重置时间推进
- 新增 ComputeQuotaResetAt / ValidateQuotaResetConfig 等辅助函数
- DTO 层新增相关字段并在 mappers 中完整映射
- 前端 QuotaLimitCard 新增 rolling/fixed 切换 UI、时区选择器
- CreateAccountModal / EditAccountModal 透传新配置字段
- i18n（zh/en）同步新增相关翻译词条

frontend/src/components/account/AccountUsageCell.vue

@@ -848,11 +848,23 @@ const makeQuotaBar = (
   let resetsAt: string | null = null
   if (startKey) {
     const extra = props.account.extra as Record<string, unknown> | undefined
-    const startStr = extra?.[startKey] as string | undefined
-    if (startStr) {
-      const startDate = new Date(startStr)
-      const periodMs = startKey.includes('daily') ? 24 * 60 * 60 * 1000 : 7 * 24 * 60 * 60 * 1000
-      resetsAt = new Date(startDate.getTime() + periodMs).toISOString()
+    const isDaily = startKey.includes('daily')
+    const mode = isDaily
+      ? (extra?.quota_daily_reset_mode as string) || 'rolling'
+      : (extra?.quota_weekly_reset_mode as string) || 'rolling'
+
+    if (mode === 'fixed') {
+      // Use pre-computed next reset time for fixed mode
+      const resetAtKey = isDaily ? 'quota_daily_reset_at' : 'quota_weekly_reset_at'
+      resetsAt = (extra?.[resetAtKey] as string) || null
+    } else {
+      // Rolling mode: compute from start + period
+      const startStr = extra?.[startKey] as string | undefined
+      if (startStr) {
+        const startDate = new Date(startStr)
+        const periodMs = isDaily ? 24 * 60 * 60 * 1000 : 7 * 24 * 60 * 60 * 1000
+        resetsAt = new Date(startDate.getTime() + periodMs).toISOString()
+      }
     }
   }
   return { utilization, resetsAt }