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

data/README.md

@@ -0,0 +1,68 @@
+# Capsule User Data Directory
+
+This directory contains all your encrypted budget data.
+
+## What's Stored Here
+
+- **users.json** - User credentials (SHA-256 hashed passwords)
+- **{userId}.json** - Individual user budget data (AES-GCM encrypted)
+- **locks/** - File locks for concurrent access protection
+
+## Data Persistence
+
+✅ This directory is **mounted as a Docker volume**  
+✅ Data persists across container restarts  
+✅ Data persists across container rebuilds  
+✅ Data survives system reboots  
+
+## Backup
+
+**Recommended:** Back up this entire directory regularly
+
+```bash
+# From parent directory
+tar -czf capsule-backup-$(date +%Y%m%d).tar.gz data/
+```
+
+## Security
+
+- All budget data is encrypted with AES-GCM
+- Passwords are hashed with SHA-256
+- NEVER share your ENCRYPTION_KEY
+- Keep this directory secure
+
+## File Structure
+
+```
+data/
+├── users.json              # User accounts
+├── user-abc123.json        # User 1 data (encrypted)
+├── user-def456.json        # User 2 data (encrypted)
+└── locks/                  # File locks
+    ├── users.json.lock
+    └── ...
+```
+
+## Troubleshooting
+
+**Data not persisting?**
+
+Check Docker volume mount:
+```bash
+docker inspect capsule-budget | grep -A 10 "Mounts"
+```
+
+Should show:
+```json
+"Mounts": [{
+    "Source": "/path/to/capsule/data",
+    "Destination": "/app/data"
+}]
+```
+
+**Permission issues?**
+
+Ensure directory has correct permissions:
+```bash
+chmod 755 data
+```