CORS/CSP hardening & centralization

- Add reusable Nginx include: roles/sys-svc-proxy/templates/headers/access_control_allow.conf.j2
  (dynamic ACAO/credentials/methods/headers via role vars)
- Set global 'Vary: Origin' in nginx.conf.j2 to prevent cache poisoning
- CSP: allow Simple Icons via connect-src when feature is enabled
- Front proxy: rename vars to lowercase + flush handlers after config deploy
- Desktop: gate & load Simple Icons role; inject brand logos when enabled
- Bluesky + Logout: replace inline CORS with centralized include
- Simpleicons: public CORS (ACAO='*', no credentials), keep GET/OPTIONS, allow headers
- Taiga: adjust canonical domain to taiga.kanban.{{ PRIMARY_DOMAIN }}
- LibreTranslate: remove unused images/versions keys

Fixes: https://open.project.infinito.nexus/projects/cymais/work_packages/342/activity
Discussion: https://chatgpt.com/share/68da5e27-ffd4-800f-91a3-0ef103058d44

roles/web-svc-simpleicons/config/main.yml

@@ -1,8 +1,6 @@
 
 credentials: {}
 docker:
-  images: {}                # @todo Move under services
-  versions: {}              # @todo Move under services
   services:
     redis:
       enabled:      false   # Enable Redis 
@@ -11,7 +9,7 @@ docker:
 features:
   matomo:           false   # Matomo tracking isn't necessary
   css:              true    # Enable Global CSS Styling
-  desktop: true    # Enable loading of app in iframe
+  desktop:          true    # Enable loading of app in iframe
   ldap:             false   # Enable LDAP Network
   central_database: false   # Enable Central Database Network
   recaptcha:        false   # Enable ReCaptcha