Add Nextcloud data directory migration workflow

Co-Authored-By: Oz <oz-agent@warp.dev>

README.md

@@ -31,6 +31,29 @@ cp .env.example .env
 ```bash
 ./scripts/test.sh
 ```
+## Move Nextcloud data directory to external storage
+Use the migration helper to move existing data to a host path and switch the app to a bind mount.
+Default target:
+- `/media/rbhat/DATA/nextcloud/NextCloudData`
+Run migration:
+```bash
+./scripts/migrate-data-directory.sh /media/rbhat/DATA/nextcloud/NextCloudData
+```
+What the script does:
+- enables maintenance mode
+- copies current `/var/www/html/data` content to target directory
+- applies owner/group and permissions for Nextcloud (`www-data`)
+- updates `docker-compose.yml` app volume with `...:/var/www/html/data`
+- recreates `app` and `web` services
+- disables maintenance mode and verifies mount
+Rollback (if needed):
+1. Remove the `:/var/www/html/data` bind mount line from `app` volumes in `docker-compose.yml`.
+2. `docker compose up -d app web`
+3. Confirm status:
+```bash
+docker exec --user www-data nextcloud-app php occ status
+```
+
 ## Production TLS (Let's Encrypt + Cloudflare DNS-01)
 1. Export credentials in shell:
 ```bash