fix: 添加混合渠道警告确认框和过滤 prompt_cache_retention 参数

- 前端: EditAccountModal 和 CreateAccountModal 添加 409 mixed_channel_warning 处理
- 前端: 弹出确认框让用户确认混合渠道风险
- 后端: 过滤 OpenAI 请求中的 prompt_cache_retention 参数（上游不支持）
- 添加中英文翻译

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',
+      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',
       apiKeyIsRequired: 'API Key is required',

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',
+      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',
       apiKeyIsRequired: 'API Key 是必需的',