Refactor yay update handling:

- Move AUR update task into dev-yay role
- Centralize defaults (AUR_HELPER, AUR_BUILDER_USER, etc.)
- Remove separate update-yay role (redundant)

See conversation with ChatGPT https://chatgpt.com/share/68da3219-6d78-800f-92ad-0a5061bac8be and related work item:
https://open.project.infinito.nexus/projects/cymais/work_packages/341/activity

roles/update-compose/tasks/01_core.yml

@@ -13,22 +13,3 @@
   include_role:
     name: update-apt
   when: ansible_distribution == "Debian"
-
-- name: "Check if yay is installed"
-  command: which yay
-  register: yay_installed
-  changed_when: false
-  failed_when: false
-
-- name: "Update with yay"
-  include_role:
-    name: update-yay
-  when:
-    - yay_installed.rc == 0
-    - run_once_update_yay is not defined
-
-- name: "Check if pkgmgr command is available"
-  command: "which pkgmgr"
-  register: pkgmgr_available
-  failed_when: false
-