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-logout/tasks/01_core.yml

@@ -21,6 +21,11 @@
 - name: "load docker, proxy for '{{ application_id }}'"
   include_role:
     name: sys-stk-full-stateless
+  vars:
+      aca_origin:       "'{{ domains | get_url('web-svc-logout', WEB_PROTOCOL) }}' always"
+      aca_credentials:  "'true' always"
+      aca_methods:      "'GET, OPTIONS' always"
+      aca_headers:      "'Accept, Authorization' always"
 
 - name: Create symbolic link from .env file to repository
   file: