fix(semaphore): make host-agnostic by omitting SEMAPHORE_WEB_ROOT

The SPA was rendering <base href="https://semaphore.local.mk-labs.cloud/">
regardless of which hostname served the page, causing the imagineering
alias to load the same UI but rewrite all in-page navigation back to the
semaphore hostname. Confusing for users hitting either Traefik alias.

Leave SEMAPHORE_WEB_ROOT empty so Semaphore emits relative URLs and is
fully host-agnostic. Both DNS names (semaphore + imagineering) now serve
cleanly without preference between them.

The template only emits SEMAPHORE_WEB_ROOT when the variable is set, so
the env-var is absent from the container when not needed.

ansible/roles/semaphore/templates/semaphore.container.j2

@@ -39,7 +39,10 @@ Environment=SEMAPHORE_PLAYBOOK_PATH=/var/lib/semaphore/playbooks
 Environment=SEMAPHORE_ACCESS_KEY_ENCRYPTION={{ semaphore_access_key_encryption }}
 
 # Public-facing URL used for OIDC redirects, webhooks, etc.
+# Empty string keeps Semaphore host-agnostic (relative URLs).
+{% if semaphore_web_url | length > 0 %}
 Environment=SEMAPHORE_WEB_ROOT={{ semaphore_web_url }}
+{% endif %}
 
 # Timezone matches host baseline
 Environment=TZ=America/Chicago