fix(bookstack): set APP_KEY so init no longer halts (docs.ginnoir.com 502)

linuxserver/bookstack refuses to start without APP_KEY:
  'The application key is missing, halting init!'
nginx never bound :80, so caddy -> bookstack:80 -> connection refused -> 502.

Key generated via 'docker run --rm --entrypoint /bin/bash
lscr.io/linuxserver/bookstack:latest appkey' on valhalla. Stored in
stacks/dev/.env per per-stack secrets policy; do NOT rotate without
invalidating existing sessions.

stacks/dev/.env

@@ -8,6 +8,8 @@ GITEA_DB_PASSWORD=gitea_d3vp4ss_9f2k
 CODE_SERVER_PASSWORD=c0de_s3rver_pass
 
 # BookStack wiki
+# APP_KEY encrypts session data — DO NOT rotate without invalidating sessions.
+BOOKSTACK_APP_KEY=base64:cSR6L4TPEbM2IFi9MyZcnmexvzAlIHAjn/qMzQKO/t4=
 BOOKSTACK_DB_PASSWORD=bookstack_d3v_pass
 BOOKSTACK_DB_ROOT_PASSWORD=bookstack_r00t_pass
 

stacks/dev/docker-compose.yml

@@ -118,6 +118,7 @@ services:
       - PGID=1000
       - TZ=${TZ}
       - APP_URL=https://docs.ginnoir.com
+      - APP_KEY=${BOOKSTACK_APP_KEY}
       - DB_HOST=mariadb_bookstack
       - DB_PORT=3306
       - DB_USER=bookstack