bookstack: 25.02.2 -> 26.05.2 [MAJOR], mariadb 11.6 -> 12.3 [MAJOR]

MAJOR (bookstack): v26.05 needs storage/fonts writable for PDF export; revision
viewing is now a separate permission. Fresh deploys unaffected; flagged for the
future in-place update path.
MAJOR (mariadb): 11.6 -> 12.3.

Campaign 7 catalog sweep.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01Nn3VgQk9iwEGgyx6QJ2NvE

templates/bookstack/docker-compose.yml

@@ -10,7 +10,7 @@
 
 services:
   bookstack:
-    image: lscr.io/linuxserver/bookstack:25.02.2
+    image: lscr.io/linuxserver/bookstack:26.05.2
     container_name: bookstack
     restart: unless-stopped
     depends_on:
@@ -51,7 +51,7 @@ services:
       - "traefik.http.services.bookstack.loadbalancer.server.port=80"
 
   bookstack-db:
-    image: mariadb:11.6
+    image: mariadb:12.3
     container_name: bookstack-db
     restart: unless-stopped
     environment: