docs(node): name the exact Ansible command that applies the pin, not 'run the play'

Node configuration in this project is Ansible's — declared in the inventory, reviewed,
version-controlled — and for prod it is the ONLY surface: infra/PROD-PROVISIONING.md
records prod as 3x bare metal with the dev OpenTofu -> Proxmox -> cloud-init path
explicitly not applying, so there is no tofu/cloud-init half to keep in parity for an
/etc/hosts pin.

The pin was already in the right place; what the docs lacked was the command. All four
places now carry the scoped, idempotent one:

    cd infra/ansible && ansible-playbook playbooks/node-baseline.yml \
      -e k3s_hosts=k3s_prod --tags hosts

--tags hosts runs ONLY the /etc/hosts task, so applying this pin cannot drift any other
baseline setting.

Also verified the mechanism is not inert, which is the failure mode this repo keeps
meeting: roles/node_baseline/tasks/main.yml renders node_baseline_hosts_pins into a marked
blockinfile with backup: true, and state: absent when the list empties — so a removed
entry really does leave the node.

Co-Authored-By: Claude Opus 5 (1M context) <[email protected]>

docs/plans/pm-agent-issue-to-pr.md

@@ -239,7 +239,8 @@ about runtime behaviour in this document is a design claim, not a measurement.
    (i) the nodes resolved the registry hostname to the WAN IP and failed TLS against the
    router's `CN=%D` placeholder certificate — **diagnosed and fixed** by pinning
    `gitea.{{ k3s_base_domain }}` to the Gateway VIP in `node_baseline_hosts_pins`, the same
-   pin the Keycloak issuer already carries; an operator must run the `node_baseline` play;
+   pin the Keycloak issuer already carries, applied by
+   `ansible-playbook playbooks/node-baseline.yml -e k3s_hosts=k3s_prod --tags hosts`;
    (ii) the pull is still unauthenticated and no `imagePullSecret` exists in the tree — with
    the credential decision now being local Gitea accounts with PATs, that means a
    `dockerconfigjson` for an account whose token carries `read:package`. Only then does the