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/i18n/locales/en.ts

@@ -1830,6 +1830,23 @@ export default {
       quotaWeeklyLimitHint: 'Automatically resets every 7 days from first usage.',
       quotaTotalLimit: 'Total Limit',
       quotaTotalLimitHint: 'Cumulative spending limit. Does not auto-reset — use "Reset Quota" to clear.',
+      quotaResetMode: 'Reset Mode',
+      quotaResetModeRolling: 'Rolling Window',
+      quotaResetModeFixed: 'Fixed Time',
+      quotaResetHour: 'Reset Hour',
+      quotaWeeklyResetDay: 'Reset Day',
+      quotaResetTimezone: 'Reset Timezone',
+      quotaDailyLimitHintFixed: 'Resets daily at {hour}:00 ({timezone}).',
+      quotaWeeklyLimitHintFixed: 'Resets every {day} at {hour}:00 ({timezone}).',
+      dayOfWeek: {
+        monday: 'Monday',
+        tuesday: 'Tuesday',
+        wednesday: 'Wednesday',
+        thursday: 'Thursday',
+        friday: 'Friday',
+        saturday: 'Saturday',
+        sunday: 'Sunday',
+      },
       quotaLimitAmount: 'Total Limit',
       quotaLimitAmountHint: 'Cumulative spending limit. Does not auto-reset.',
       testConnection: 'Test Connection',