docs

This commit enhances the node removal playbook's reliability and safety by implementing the following changes:

1. **Node Validation**: Added a validation step using assert to ensure the `node` variable is defined and contains nodes. If the list is empty or undefined, the playbook fails early, preventing accidental operations on the entire cluster.

2. **Removed Defaulting for Hosts**: Updated tasks to enforce explicit `node` variable input without defaulting to critical groups (e.g., `etcd:k8s_cluster:calico_rr`). By validating `node` beforehand, tasks now solely rely on user-provided input and safely avoid unintended targeting.

3. **Explicit User Confirmation**: Enhanced the confirmation prompt to clarify the scope of the operation. The admin is now required to explicitly confirm node state deletion, ensuring a deliberate decision before proceeding.

These improvements strengthen the reliability and safety of the `remove-node.yml` playbook by eliminating ambiguous behavior, preventing misconfigurations, and ensuring clear interaction during node removal tasks.