fix: properly display API error response body for 400 errors

Previously, ApiError instances were being re-wrapped, causing the responseBody
to be lost and showing nested error messages like "API Error: Error from OpenAI:
Error: API Error: Status Code 400" instead of the actual error details.

Now ApiError instances are passed through without re-wrapping, ensuring the
responseBody is preserved and displayed correctly in MessageErrTips.

🤖 Generated with [Claude Code](https://claude.ai/code)

Co-Authored-By: Claude <noreply@anthropic.com>

Author: themez

src/shared/models/abstract-ai-sdk.ts

@@ -389,6 +389,9 @@ export default abstract class AbstractAISDKModel implements ModelInterface {
     if (APICallError.isInstance(error)) {
       throw new ApiError(`Error from ${this.name}${context}`, error.responseBody)
     }
+    if (error instanceof ApiError) {
+      throw error
+    }
     if (error instanceof ChatboxAIAPIError) {
       throw error
     }