refactor: use module_defaults for proxmox API connection

- Replace YAML merge keys (<<:) with module_defaults block in main.yml
- Simplify connection variables to individual vars instead of dictionary
- Remove redundant connection params from individual task files
- Document standalone task usage requires play-level module_defaults
- Update README examples with new variable pattern

roles/proxmox_lxc_provision/tasks/convert.yml

@@ -1,8 +1,7 @@
 ---
-- ansible.builtin.include_tasks: stop.yaml
+- ansible.builtin.include_tasks: stop.yml
+
 - name: Convert container to template
   community.general.proxmox:
-    <<: "{{ proxmox_api_connection }}"
-
-    state: template
     hostname: "{{ lxc_hostname }}"
+    state: template