[UX][i18n] Replace raw engine errors with user-friendly guidance when no models are available

[shangxinyu1]

Environment

Platform: Cross-platform (Desktop/Web)
Version: 0.1.12-nightly.20260415
Component: Agent Error Handling / Runtime Feedback

Description

Currently, when a user is logged out or hasn't configured an API key, the system displays a raw, technical error message from the underlying engine (OpenClaw).

Current Raw Error Example:
Agent failed before reply: No API key found for provider "anthropic". Auth store: /Users/mac/Library/... Configure auth for this agent (openclaw agents add <id>)... Logs: openclaw logs --follow

This is poor UX as it:

1. Exposes internal file system paths.
2. Mentions developer-centric CLI commands (openclaw agents add) that end-users won't understand.
3. Fails to provide a clear "Golden Path" for recovery.

Proposed UX Improvements

We should intercept these raw engine errors and replace them with localized, actionable guidance:

New Copy (Chinese):
"未检测到可用模型。您可以[立即登录]以获取 Nexu 免费模型，或前往[设置-模型]配置您的自定义模型。"

New Copy (English):
"No available models found. Please [Log In] to use free models, or configure your own in [Settings - Models]."

Impact

Severity: P1 (High) - UX Standard.

• Prevents user confusion and fear of "broken" systems.
• Improves conversion to login/sign-up.
• Protects internal system privacy (file paths).

Screenshot

[nexu-io]

AI Translation

Only the non-English parts are translated below.

Translated sections:

New Copy (Chinese)::

"No available models detected. You can [Log in now] to get Nexu free models, or go to [Settings - Models] to configure your custom models."