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/group_vars/traefik_servers/traefik.yml

@@ -2,6 +2,7 @@ _acme_tsig: "{{ lookup('community.hashi_vault.hashi_vault', vault_mount + '/data
 
 traefik_use_ssl: true
 traefik_cert_mode: "acme"
+traefik_ssl_email: "hostmaster@digitalboard.ch"
 traefik_log_level: DEBUG
 traefik_network: proxy
 
@@ -11,3 +12,9 @@ traefik_acme_tsig_algorithm: "hmac-sha256"
 traefik_acme_tsig_key: "{{ _acme_tsig.tsig_key }}"
 traefik_acme_tsig_secret: "{{ _acme_tsig.tsig_secret }}"
 
+# UDP/53 egress from the traefik container reaches ns1.digitalboard.ch
+# unreliably (i/o timeouts on lego's recursive SOA pre-check), while
+# TCP/53 to the same nameserver is open. Force lego to do its DNS
+# lookups over TCP so the DNS-01 challenge can proceed.
+traefik_acme_tcp_only: true
+