feat(bookstack): add role for self-hosted BookStack deployment

Deploy BookStack with linuxserver.io images behind Traefik, including
Entra ID OIDC SSO support and a daily backup timer.

Stack:
- lscr.io/linuxserver/bookstack:version-v26.03.3
- lscr.io/linuxserver/mariadb:11.4.9
- Traefik labels for websecure entrypoint on internal network
- Healthcheck via mariadb-admin ping (LSIO image lacks healthcheck.sh)

Features:
- Persistent APP_KEY generated on first run, stored in volume dir
- Optional OIDC SSO via Microsoft Entra ID (configurable per-instance)
- Idempotent admin user creation with DB-based existence check
- Daily systemd timer backup (DB dump + uploads tar + APP_KEY)
  with configurable retention

Implementation notes:
- DB queries use --protocol=tcp with the app user because root@localhost
  uses unix_socket auth in the LSIO MariaDB image (no password) and
  root@% does not exist
- docker_container_exec uses argv: (list) instead of command: (string)
  to avoid argument-splitting issues
- Migration-wait task ensures users table exists before admin check,
  since /login returns 200 before Laravel migrations complete
- no_log: true on all tasks that reference DB or admin passwords
- artisan absolute path (/app/www/artisan) because LSIO image WORKDIR
  is not the app directory

Adds bookstack route to DMZ Traefik service registry.

inventories/vagrant/hosts.yml

@@ -85,6 +85,6 @@ all:
       hosts:
         backend:
 
-    opnform_servers:
+    bookstack_servers:
       hosts:
         backend: