Adding code for app.py and updating requirements.txt

app.py

@@ -13,7 +13,7 @@ class URLValidator:
 
     def __init__(self):
         # API Keys
-        self.serpapi_key = os.genenv('SERPAPI_KEY')
+        self.serpapi_key = os.getenv('SERPAPI_KEY')
         self.google_safe_browsing_key = os.getenv('GOOGLE_SAFE_KEY')
 
         # Load models once to avoid redundant API calls