added default .env.example

.env.example

@@ -0,0 +1,11 @@
+# Example .env file for SlideDeck AI
+# Add your API keys and configuration values here
+
+# OpenRouter API key (if using OpenRouter as a provider)
+
+OPENROUTER_API_KEY=your-openrouter-api-key
+# Optional: Site metadata for OpenRouter ranking (see docs)
+OPENROUTER_SITE_URL=http://localhost:8501
+OPENROUTER_SITE_NAME=SlideDeck AI
+
+STREAMLIT_SERVER_RUN_ON_SAVE=true