fix(web-app-mastodon,web-app-peertube): loop the vhosts without shadowing domain

tasks/utils/load/app.yml hands every loaded application `domain` as an
include var, so the vhost loops of Mastodon and PeerTube, which named
their item `domain`, made Ansible warn "The loop variable 'domain' is
already in use" (full-6 once, full-7 three times, full-8 twice). The loops
now name the item front_proxy_vhost and pass it to sys-stk-front-proxy as
`domain` in the include vars, which is the name its tasks/main.yml reads;
the two loop-var-shadow suppressions go with the shadowing.

Evidence: a stub playbook with an outer `domain` include var and a nested
include reproduces the warning with the old shape and shows none with the
new one; both shapes deliver each vhost to the outer and the nested role,
and the outer `domain` is intact after the loop.

Co-Authored-By: Claude Opus 5.5 (1M context) <noreply@anthropic.com>

roles/web-app-mastodon/tasks/00_core.yml

@@ -1,13 +1,14 @@
 ---
 - include_tasks: utils/once/flag.yml
 
-- name: "📂 Include setup for domain '{{ domain }}'"
+- name: "📂 Include the front proxy for every {{ application_id }} domain"
   include_role:
     name: sys-stk-front-proxy
   loop: "{{ lookup('domains', 'web-app-mastodon') }}"
   loop_control:
-    loop_var: domain # nocheck: loop-var-shadow  sys-stk-front-proxy takes the vhost through this name, see its tasks/main.yml front_proxy_domain
+    loop_var: front_proxy_vhost
   vars:
+    domain: "{{ front_proxy_vhost }}"
     http_port: "{{ lookup('config', application_id, 'services.mastodon.ports.local.http') }}"
     webserver_websocket_location: "/api/v1/streaming"
     websocket_port: "{{ lookup('config', application_id, 'services.mastodon.ports.local.websocket') }}"

roles/web-app-peertube/tasks/00_core.yml

@@ -1,13 +1,14 @@
 ---
 - include_tasks: utils/once/flag.yml
 
-- name: "📂 Include front proxy for domain '{{ domain }}'"
+- name: "📂 Include the front proxy for every {{ application_id }} domain"
   include_role:
     name: sys-stk-front-proxy
   loop: "{{ lookup('domains', application_id) }}"
   loop_control:
-    loop_var: domain # nocheck: loop-var-shadow  sys-stk-front-proxy takes the vhost through this name, see its tasks/main.yml front_proxy_domain
+    loop_var: front_proxy_vhost
   vars:
+    domain: "{{ front_proxy_vhost }}"
     http_port: "{{ lookup('config', application_id, 'services.peertube.ports.local.http') }}"
     websocket_port: "{{ lookup('config', application_id, 'services.peertube.ports.local.http') }}"