Add comprehensive data persistence verification

- Added test-persistence.sh script to verify Docker volume mounting
- Enhanced DEPLOYMENT.md with detailed data persistence documentation
- Updated deploy.sh to verify data directory mount on deployment
- Added data/README.md explaining data storage and backup
- Updated data/.gitignore to include README.md
- Documented what data persists and what doesn't
- Added backup strategies and troubleshooting tips

data/.gitignore

@@ -1,5 +1,6 @@
 # Exclude all user data files
 *.json
 
-# Keep this .gitignore file
+# Keep these files
 !.gitignore
+!README.md