chore(demo-gymburgdorf): finish ACME, LDAP, DMZ routing for live inventory

- ACME via DNS-01 against internal NS (172.16.9.169) with TCP-only +
  disableANSChecks so the DMZ traefik can issue LE certs without
  reaching public NS IPs.
- Migrate single-domain vars to `*_domains` lists (authentik, nextcloud,
  collabora, garage_s3) so public + *.int.* SANs share one cert and
  server-to-server traffic stays in the LAN.
- Wire `traefik_dmz_exposed_services` per backend host (application,
  storage) with explicit `backend_host` overrides pointing at internal
  FQDNs — DMZ traefik now validates upstream certs against SAN names.
- Nextcloud notify_push setup on internal FQDN to avoid DMZ hairpin;
  collabora WOPI / authentik LDAP outpost wired to *.int.* equivalents.

inventories/demo-gymburgdorf/host_vars/application/authentik.yml

@@ -5,7 +5,13 @@
 #   nextcloud_oidc_secret
 _authentik: "{{ lookup('community.hashi_vault.hashi_vault', vault_mount + '/data/authentik', url=vault_addr) }}"
 
-authentik_domain: "auth.gymb.souveredu.ch"
+# First entry is the canonical public FQDN. Additional entries cover
+# internal *.int.* names so server-to-server traffic (e.g. the LDAP
+# outpost) hits authentik on a name with a valid internal cert and
+# skips the DMZ hop.
+authentik_domains:
+  - "auth.gymb.souveredu.ch"
+  - "auth.int.gymb.souveredu.ch"
 authentik_secret_key: "{{ _authentik.secret_key }}"
 authentik_postgres_password: "{{ _authentik.postgres_password }}"
 
@@ -20,7 +26,9 @@ authentik_ldap_outpost:
   name: "ldap-outpost"
   token: "{{ _authentik.ldap_outpost_token }}"
   config:
-    authentik_host: "https://auth.gymb.souveredu.ch/"
+    # Outpost pulls config from authentik over the internal FQDN — keeps
+    # the round-trip in the LAN with a valid cert.
+    authentik_host: "https://auth.int.gymb.souveredu.ch/"
     log_level: "info"
 
 # OIDC clients