feat: websearch quota enhancements and balance notify hint

- QuotaLimit changed to *int64 (null=unlimited, >0=limited)
- Add reset-usage endpoint (POST /admin/settings/web-search-emulation/reset-usage)
- Show quota usage in header always (collapsed and expanded)
- Add reset quota button in expanded provider view
- Quota input: empty=unlimited with ∞ placeholder, must be >0 if set
- Add email verification hint on balance notify card

frontend/src/i18n/locales/en.ts

@@ -914,6 +914,7 @@ export default {
       thresholdPlaceholder: 'Enter amount',
       systemDefault: 'System Default',
       extraEmails: 'Notification Emails',
+      extraEmailsHint: 'You must add and verify an email address to receive low balance alerts',
       primaryEmail: 'Primary',
       noExtraEmails: 'No extra notification emails',
       enterEmail: 'Enter email address',
@@ -4435,10 +4436,14 @@ export default {
         copyApiKey: 'Copy',
         copied: 'Copied',
         quotaLimit: 'Quota Limit',
-        quotaLimitHint: '0 = unlimited',
+        quotaLimitHint: 'Leave empty for unlimited; must be > 0 if set',
+        quotaLimitMustBePositive: 'Quota limit must be greater than 0',
         subscribedAt: 'Subscribed At',
-        subscribedAtHint: 'Quota resets monthly from this date',
+        subscribedAtHint: 'Quota resets monthly from this date; leave empty to disable auto-reset',
         quotaUsage: 'Usage',
+        resetUsage: 'Reset',
+        resetUsageConfirm: 'Reset usage counter for this provider?',
+        resetUsageSuccess: 'Usage counter reset',
         proxy: 'Proxy',
         removeProvider: 'Remove',
         noProviders: 'No search providers configured',

frontend/src/i18n/locales/zh.ts

@@ -918,6 +918,7 @@ export default {
       thresholdPlaceholder: '输入金额',
       systemDefault: '系统默认值',
       extraEmails: '通知邮箱',
+      extraEmailsHint: '必须添加并验证邮箱后，余额不足时才能收到提醒邮件',
       primaryEmail: '主邮箱',
       noExtraEmails: '暂无额外通知邮箱',
       enterEmail: '输入邮箱地址',
@@ -4597,10 +4598,14 @@ export default {
         copyApiKey: '复制',
         copied: '已复制',
         quotaLimit: '配额上限',
-        quotaLimitHint: '0 表示无限制',
+        quotaLimitHint: '留空表示无限制；填写时必须大于 0',
+        quotaLimitMustBePositive: '配额上限必须大于 0',
         subscribedAt: '订阅时间',
-        subscribedAtHint: '配额从此日期起每月自动重置',
+        subscribedAtHint: '配额从此日期起每月自动重置；留空则不自动重置',
         quotaUsage: '用量',
+        resetUsage: '重置',
+        resetUsageConfirm: '确定要重置此服务商的用量计数吗？',
+        resetUsageSuccess: '用量已重置',
         proxy: '代理',
         removeProvider: '删除',
         noProviders: '未配置搜索服务商',