Retire Authentik now that every app logs in with Pocket ID

All of Authentik's applications (including Tailscale's tailnet login)
have moved to Pocket ID, and its only recent sign-ins were those
handovers. Drops its stack, the auth. route and DNS record, the auth
subdomain variables, Gotify's leftover hairpin entries, and the dockcheck
exclude; the docs now name Pocket ID as the SSO provider.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

roles/docker/templates/gotify-compose.yml.j2

@@ -11,7 +11,6 @@ services:
     labels:
       mag37.dockcheck.update: true
     extra_hosts:
-      - "{{ subdomains.auth }}:{{ docker.hairpin_ip }}"
       - "{{ subdomains.gotify_assistant }}:{{ docker.hairpin_ip }}"
 
   igotify-assistant:
@@ -27,7 +26,6 @@ services:
     labels:
       mag37.dockcheck.update: true
     extra_hosts:
-      - "{{ subdomains.auth }}:{{ docker.hairpin_ip }}"
       - "{{ subdomains.gotify }}:{{ docker.hairpin_ip }}"
 
 volumes: