fix(i18n): correct insufficient balance error hint text

Remove misleading "upstream" wording - the error is about client API key
user balance, not upstream account balance.

frontend/src/i18n/locales/en.ts

@@ -3843,7 +3843,7 @@ export default {
         ignoreInvalidApiKeyErrors: 'Ignore invalid API key errors',
         ignoreInvalidApiKeyErrorsHint: 'When enabled, invalid or missing API key errors (INVALID_API_KEY, API_KEY_REQUIRED) will not be written to the error log.',
         ignoreInsufficientBalanceErrors: 'Ignore Insufficient Balance Errors',
-        ignoreInsufficientBalanceErrorsHint: 'When enabled, upstream insufficient account balance errors will not be written to the error log.',
+        ignoreInsufficientBalanceErrorsHint: 'When enabled, insufficient account balance errors will not be written to the error log.',
         autoRefresh: 'Auto Refresh',
         enableAutoRefresh: 'Enable auto refresh',
         enableAutoRefreshHint: 'Automatically refresh dashboard data at a fixed interval.',

frontend/src/i18n/locales/zh.ts

@@ -4017,7 +4017,7 @@ export default {
         ignoreInvalidApiKeyErrors: '忽略无效 API Key 错误',
         ignoreInvalidApiKeyErrorsHint: '启用后，无效或缺失 API Key 的错误（INVALID_API_KEY、API_KEY_REQUIRED）将不会写入错误日志。',
         ignoreInsufficientBalanceErrors: '忽略余额不足错误',
-        ignoreInsufficientBalanceErrorsHint: '启用后，上游账号余额不足（Insufficient balance）的错误将不会写入错误日志。',
+        ignoreInsufficientBalanceErrorsHint: '启用后，账号余额不足（Insufficient balance）的错误将不会写入错误日志。',
         autoRefresh: '自动刷新',
         enableAutoRefresh: '启用自动刷新',
         enableAutoRefreshHint: '自动刷新仪表板数据，启用后会定期拉取最新数据。',