refactor: 使用 ConfirmDialog 组件替代原生 confirm() 对话框

- EditAccountModal 和 CreateAccountModal 使用 ConfirmDialog 组件
- 保存 pending payload 供确认后重试
- 添加 mixedChannelWarningTitle 翻译

Co-authored-by: factory-droid[bot] <138933559+factory-droid[bot]@users.noreply.github.com>

frontend/src/i18n/locales/en.ts

@@ -1306,6 +1306,7 @@ export default {
       accountUpdated: 'Account updated successfully',
       failedToCreate: 'Failed to create account',
       failedToUpdate: 'Failed to update account',
+      mixedChannelWarningTitle: 'Mixed Channel Warning',
       mixedChannelWarning: 'Warning: Group "{groupName}" contains both {currentPlatform} and {otherPlatform} accounts. Mixing different channels may cause thinking block signature validation issues, which will fallback to non-thinking mode. Are you sure you want to continue?',
       pleaseEnterAccountName: 'Please enter account name',
       pleaseEnterApiKey: 'Please enter API Key',

frontend/src/i18n/locales/zh.ts

@@ -1439,6 +1439,7 @@ export default {
       accountUpdated: '账号更新成功',
       failedToCreate: '创建账号失败',
       failedToUpdate: '更新账号失败',
+      mixedChannelWarningTitle: '混合渠道警告',
       mixedChannelWarning: '警告：分组 "{groupName}" 中同时包含 {currentPlatform} 和 {otherPlatform} 账号。混合使用不同渠道可能导致 thinking block 签名验证问题，会自动回退到非 thinking 模式。确定要继续吗？',
       pleaseEnterAccountName: '请输入账号名称',
       pleaseEnterApiKey: '请输入 API Key',