feat(services): multi-domain routing, split-horizon and OIDC hardening

Bundle of cross-role changes for the gymb services deployment:

- Traefik routers: OR-combine opnform/homarr/bookstack Host rules with new
  *_extra_domains (internal *.int.* FQDNs for a DMZ reverseproxy), and emit
  tls.certresolver only when traefik_cert_mode == acme (drawio, homarr,
  opnform, send).
- Split-horizon: bookstack_extra_hosts / opnform_extra_hosts add container
  /etc/hosts overrides so containers reach the IdP public FQDN over the LAN.
- bookstack: assert the OIDC issuer resolves concretely (reject "//v2.0"),
  allowing non-Entra IdPs that override bookstack_oidc_issuer.
- homarr: derive the bcrypt salt from the password digest so the admin hash
  is idempotent — no spurious template changes / container restarts.
- opnform: PATCH an existing OIDC connection instead of skipping (applies
  corrected inventory on re-run); add OIDC_FORCE_LOGIN (enabled only after
  bootstrap) and an optional direct-SSO ingress entrypoint.

Docs: READMEs and meta/argument_specs.yml updated for all new variables.

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

@@ -50,6 +50,9 @@ services:
 {% if send_use_ssl %}
       - traefik.http.routers.{{ send_service_name }}.entrypoints=websecure
       - traefik.http.routers.{{ send_service_name }}.tls=true
+{% if traefik_cert_mode | default('selfsigned') == 'acme' %}
+      - traefik.http.routers.{{ send_service_name }}.tls.certresolver={{ traefik_ssl_cert_resolver | default('dns') }}
+{% endif %}
 {% else %}
       - traefik.http.routers.{{ send_service_name }}.entrypoints=web
 {% endif %}