Fix invalid OpenRouter model IDs

- Replace openai/gpt-4o-nano with openai/gpt-4o-mini
- Replace mistralai/mistral-medium with mistralai/mistral-7b-instruct
- Replace google/gemma-3-27b-it with meta-llama/llama-3.1-8b-instruct
- All models now use valid OpenRouter API endpoints

app.py

@@ -425,13 +425,13 @@ if __name__ == "__main__":
     demo.launch()
 '''
 
-# Available models
+# Available models - Updated with valid OpenRouter model IDs
 MODELS = [
-    "google/gemma-3-27b-it",          # Open-source, sustainable option
-    "google/gemini-2.0-flash-001",    # Fast, reliable, general tasks
-    "mistralai/mistral-medium",       # Good for technical topics
-    "openai/gpt-4o-nano",            # Balanced performance and cost
-    "anthropic/claude-3.5-haiku"     # Complex reasoning and analysis
+    "google/gemini-2.0-flash-001",      # Fast, reliable, general tasks
+    "anthropic/claude-3.5-haiku",       # Complex reasoning and analysis
+    "openai/gpt-4o-mini",               # Balanced performance and cost
+    "meta-llama/llama-3.1-8b-instruct", # Open-source, efficient option
+    "mistralai/mistral-7b-instruct"     # Good for technical topics
 ]
 
 def fetch_url_content(url):