fix: use google/medgemma-4b-it

app.py

@@ -15,7 +15,7 @@ class MedGemmaSymptomAnalyzer:
         if self.model_loaded:
             return True
             
-        model_name = "google/medgemma-2b"
+        model_name = "google/medgemma-4b-it"
         print(f"Loading model: {model_name}")
         
         try: