Update model to gpt-4.1-mini and enhance error handling in explain_concept function

app.py

@@ -75,7 +75,7 @@ def explain_concept(question, level, language):
     try:
         # Generate streaming explanation using OpenAI API
         stream = client.chat.completions.create(
-            model="gpt-4.1",
+            model="gpt-4.1-mini",
             messages=[
                 {"role": "system", "content": system_prompt},
                 {"role": "user", "content": question}
@@ -94,7 +94,18 @@ def explain_concept(question, level, language):
                 yield partial
                 
     except Exception as e:
-        yield f"❌ Error generating explanation: {str(e)}"
+        # Provide more specific error messages for common issues
+        error_msg = str(e).lower()
+        if "connection" in error_msg or "timeout" in error_msg:
+            yield "❌ Connection error: Unable to reach OpenAI API. Please check your internet connection and try again."
+        elif "api key" in error_msg or "authentication" in error_msg:
+            yield "❌ Authentication error: Invalid API key. Please check your OpenAI API key configuration."
+        elif "rate limit" in error_msg:
+            yield "❌ Rate limit exceeded: Too many requests. Please wait a moment and try again."
+        elif "model" in error_msg:
+            yield "❌ Model error: The specified model is not available. Please try again later."
+        else:
+            yield f"❌ Error generating explanation: {str(e)}"
 
 # Create enhanced Gradio interface with modern styling
 with gr.Blocks(