feat(ui): add endpoint format hint for Codex providers

Add informational hint below Codex API endpoint input field to guide users
to fill in OpenAI Response compatible service endpoints, similar to the
existing hint for Claude providers.

src/i18n/locales/zh.json

@@ -174,6 +174,7 @@
     "fastModelPlaceholder": "例如: GLM-4.5-Air",
     "modelHint": "💡 留空将使用供应商的默认模型",
     "apiHint": "💡 填写兼容 Claude API 的服务端点地址",
+    "codexApiHint": "💡 填写兼容 OpenAI Response 格式的服务端点地址",
     "fillSupplierName": "请填写供应商名称",
     "fillConfigContent": "请填写配置内容",
     "fillParameter": "请填写 {{label}}",