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/stop.yml

@@ -1,10 +1,9 @@
 ---
 - name: Stop container if it is running
   community.general.proxmox:
-    <<: "{{ proxmox_api_connection }}"
     vmid: "{{ lxc_vmid | default(omit) }}"
     hostname: "{{ lxc_hostname | default(omit) }}"
-    state: "stopped"
+    state: stopped
   register: stop_result
   failed_when: |-
     stop_result.failed and