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/tasks/infrastructure/main.yml

@@ -5,10 +5,6 @@
   import_tasks: caddy.yml
   tags: caddy
 
-- name: Install authentik
-  import_tasks: authentik.yml
-  tags: authentik
-
 - name: Install pocketid
   import_tasks: pocketid.yml
   tags: pocketid