refactor: Use Docker Compose managed volume with project prefix

Changes:
- docker-compose.yml: Change from external volume to managed volume
  - Volume name: nlcc-data → data
  - Docker Compose auto-prefixes: nlcc-itinerary_data
  - Remove external: true flag
  - Volume created automatically on first up

- README.md: Update all volume references
  - Installation: Remove manual volume creation step
  - Volume name: nlcc-data → nlcc-itinerary_data
  - Add note about automatic creation
  - Update all backup/restore/inspect commands

Benefits:
- No manual volume creation required
- Docker Compose manages lifecycle automatically
- Project-scoped volume naming (nlcc-itinerary_data)
- Cleaner deployment process (one less step)
- Volume automatically created on docker-compose up
- Consistent with Docker Compose best practices

The volume will be created as "nlcc-itinerary_data" where:
- nlcc-itinerary = project directory name
- data = volume name defined in docker-compose.yml

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

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

docker-compose.yml

@@ -5,7 +5,7 @@ services:
     ports:
       - "3002:3000"
     volumes:
-      - nlcc-data:/app/data
+      - data:/app/data
     environment:
       - NODE_ENV=production
       - SITE_URL=https://church.example.com
@@ -22,5 +22,4 @@ services:
     restart: unless-stopped
 
 volumes:
-  nlcc-data:
-    external: true
+  data: