feat: Add Hugging Face Spaces entry point

- Created app.py as HF Spaces entry point
- Imports and launches main Gradio app from web/app_gradio.py
- Maintains compatibility with HF Spaces deployment requirements

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude <noreply@anthropic.com>

app.py

@@ -0,0 +1,21 @@
+#!/usr/bin/env python3
+"""
+D&D RAG Game Master - Hugging Face Spaces Entry Point
+
+This file is the entry point for Hugging Face Spaces deployment.
+It imports and launches the main Gradio app from web/app_gradio.py
+"""
+
+import sys
+from pathlib import Path
+
+# Add project root to path
+sys.path.insert(0, str(Path(__file__).parent))
+
+# Import the main Gradio app
+from web.app_gradio import demo
+
+if __name__ == "__main__":
+    # Launch the app
+    # HF Spaces automatically detects the demo object and runs it
+    demo.launch()