Add better error handling for missing API key

app.py

@@ -23,8 +23,19 @@ logger = logging.getLogger(__name__)
 load_dotenv()
 
 # Initialize OpenAI client for Perplexity
+api_key = os.getenv('PERPLEXITY_API_KEY')
+if not api_key:
+    st.error("""
+    ⚠️ Perplexity API key not found! Please add your API key to the Space's secrets:
+    1. Go to Space Settings
+    2. Click on 'Repository secrets'
+    3. Add a new secret with name 'PERPLEXITY_API_KEY'
+    4. Add your Perplexity API key as the value
+    """)
+    st.stop()
+
 client = OpenAI(
-    api_key=os.getenv('PERPLEXITY_API_KEY'),
+    api_key=api_key,
     base_url="https://api.perplexity.ai"
 )