Make mail stack optional for Infinito.Nexus deployments without Mailu (e.g. Raspberry Pi / robots)

Refactored mail-related roles to support running Infinito.Nexus on nodes without a dedicated mail server:
- Introduced sys-svc-mail as central mail orchestration role.
- Split msmtp handling into sys-svc-mail-msmtp.
- Added sys-svc-mail-smtp to provide a localhost-only Postfix relay when Mailu is not present.
- Updated alert/health roles to use the new mail orchestration.
- Avoid installing postfix inside containers via IS_CONTAINER guard.
- Adjusted WordPress role to use the new msmtp template path.

This allows lightweight deployments (e.g. Raspberry Pi, robots, edge nodes) to send mail via localhost without requiring a full Mailu stack.

ChatGPT discussion: https://chatgpt.com/share/6931edf1-cb98-800f-9e3c-a62d69ccb223

roles/sys-ctl-hlth-msmtp/tasks/01_core.yml

@@ -1,16 +1,8 @@
-- name: Include dependency 'sys-ctl-alm-telegram'
-  include_role:
-    name: sys-ctl-alm-telegram
-  when: run_once_sys_ctl_alm_telegram is not defined
-  
 - include_role:
     name: sys-service
   vars:
     system_service_tpl_on_failure: "{{ SYS_SERVICE_ON_FAILURE_COMPOSE }}"
     system_service_on_calendar:    "{{ SYS_SCHEDULE_HEALTH_MSMTP }}"
     system_service_timer_enabled:  true
-  when:
-    - not MODE_RESET | bool
-    - users['no-reply'].mailu_token is defined
 
 - include_tasks: utils/once/flag.yml