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.

roles/bookstack/templates/backup.sh.j2

@@ -0,0 +1,41 @@
+#!/bin/bash
+# {{ ansible_managed }}
+set -euo pipefail
+
+BACKUP_DIR="{{ bookstack_backup_dir }}"
+RETENTION_DAYS={{ bookstack_backup_retention_days }}
+APPDATA_DIR="{{ bookstack_appdata_dir }}"
+STAMP="$(date +%Y%m%d-%H%M%S)"
+
+mkdir -p "$BACKUP_DIR"
+
+# --- DB dump (mariadb-dump from inside the DB container) ---
+# Use the app user via TCP because root@localhost is unix_socket-auth only
+# in the LSIO MariaDB image and root@% does not exist.
+docker exec {{ bookstack_service_name }}-db \
+  mariadb-dump \
+    --protocol=tcp -h 127.0.0.1 \
+    -u "{{ bookstack_db_user }}" -p"{{ bookstack_db_password }}" \
+    --single-transaction --routines --triggers --quick \
+    "{{ bookstack_db_name }}" \
+  | gzip -9 > "$BACKUP_DIR/bookstack-db-$STAMP.sql.gz"
+
+# --- File uploads (images, attachments) ---
+# LSIO BookStack stores user uploads under /config/www/{uploads,storage/uploads,files}.
+tar --warning=no-file-changed \
+    -czf "$BACKUP_DIR/bookstack-files-$STAMP.tar.gz" \
+    -C "$APPDATA_DIR/www" \
+    uploads storage/uploads files 2>/dev/null || true
+
+# --- APP_KEY backup (critical for restore!) ---
+install -m 0600 "{{ bookstack_docker_volume_dir }}/.app_key" \
+                "$BACKUP_DIR/bookstack-appkey-$STAMP.txt"
+
+# --- Retention ---
+find "$BACKUP_DIR" -type f \
+    \( -name 'bookstack-db-*.sql.gz' \
+    -o -name 'bookstack-files-*.tar.gz' \
+    -o -name 'bookstack-appkey-*.txt' \) \
+    -mtime +"$RETENTION_DAYS" -delete
+
+echo "Backup complete: $STAMP"