web-app-mediawiki: installer-driven bootstrap, DB readiness, idempotent admin; drop LocalSettings bind-mount

Tasks:
- Enable docker_compose_flush_handlers=true so services come up immediately.
- Add DB readiness guard via maintenance/sql.php (SELECT 1).
- Run maintenance/install.php on empty schema with robust changed_when/failed_when (merge stdout+stderr); keep secrets hidden.
- Run maintenance/update.php for migrations with neutral changed_when unless work is done.
- Make admin creation idempotent: tolerate 'already exists' and 'Account exists', keep async+no_log.

Config changes:
- Remove LocalSettings.php template and its host bind-mount from compose.
- Drop MediaWiki settings path variables and META namespace variable (unused after switch).

Result: First boot is fully automated (schema + admin), subsequent runs are cleanly idempotent.

Ref: ChatGPT conversation (Aug 28, 2025, Europe/Berlin) — https://chatgpt.com/share/68b0d2e1-9bc0-800f-81a5-db03ce0b81e3.

roles/web-app-mediawiki/vars/main.yml

@@ -5,7 +5,6 @@ container_port:                   80
 
 # Mediawiki
 MEDIAWIKI_SITENAME:               "{{ applications | get_app_conf(application_id, 'sitename') }}"
-MEDIAWIKI_META_NAMESPACE:         "{{ applications | get_app_conf(application_id, 'meta_namespace') }}"
 MEDIAWIKI_URL:                    "{{ domains | get_url(application_id, WEB_PROTOCOL) }}"
 
 ## Docker
@@ -13,8 +12,6 @@ MEDIAWIKI_VERSION:                "{{ applications | get_app_conf(application_id
 MEDIAWIKI_IMAGE:                  "{{ applications | get_app_conf(application_id, 'docker.services.mediawiki.image') }}"
 MEDIAWIKI_CONTAINER:              "{{ applications | get_app_conf(application_id, 'docker.services.mediawiki.name') }}"
 MEDIAWIKI_VOLUME:                 "{{ applications | get_app_conf(application_id, 'docker.volumes.data') }}"
-MEDIAWIKI_SETTINGS_HOST_PATH:     "{{ [docker_compose.directories.volumes, 'LocalSettings.php'] | path_join }}"
-MEDIAWIKI_SETTINGS_DOCK_PATH:     "/var/www/html/LocalSettings.php"
 MEDIAWIKI_USER:                   "www-data"
 
 # User