fix(semaphore): provide SEMAPHORE_ADMIN_* env vars for non-interactive first boot

The v2.18 image's entrypoint runs the setup wizard on first boot. Without
the SEMAPHORE_ADMIN_* variables it prompts on stdin, fails with 'Username
cannot be empty', and the container exits — leading to a crash loop.

Set:
  SEMAPHORE_ADMIN=admin
  SEMAPHORE_ADMIN_NAME=Administrator
  SEMAPHORE_ADMIN_EMAIL=admin@local.mk-labs.cloud
  SEMAPHORE_ADMIN_PASSWORD={{ vault_semaphore_admin_password }}
  SEMAPHORE_PLAYBOOK_PATH=/var/lib/semaphore/playbooks

The env-var bootstrap path is stable in v2.x; only the legacy
'semaphore user add' CLI invocation was unreliable. Drop the manual
user-add step from the README.

ansible/roles/semaphore/tasks/verify.yml

@@ -22,9 +22,5 @@
     msg: >-
       Semaphore is reachable on http://127.0.0.1:{{ semaphore_listen_port }}.
       Public URL: {{ semaphore_web_url }}.
-      If this is the first deployment, create the admin user with:
-        sudo podman exec -it {{ semaphore_container_name }} \
-          semaphore user add --admin \
-            --login admin --name Administrator \
-            --email admin@local.mk-labs.cloud \
-            --password '<see vault_semaphore_admin_password>'
+      Admin user 'admin' is provisioned automatically on first boot using
+      vault_semaphore_admin_password.