Sync docs after playbook/structure changes

- ansible/README.md: drop removed shutdown playbook mention
- CLAUDE.md: list nvidia_gpu under custom roles
- sftp README: link the config notes

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

ansible/README.md

@@ -7,7 +7,7 @@ Global configuration for all Phytron servers. Run everything from this directory
 - `hosts.ini` — inventory; one group per host (`phy_z_*`), host aliases match the real hostnames
 - `group_vars/all.yml` — defaults for all hosts; `group_vars/<group>.yml` holds per-host overrides only
 - `group_vars/secrets.yml` — ansible-vault encrypted secrets
-- `run.yml` — main playbook; `playbooks/` — utilities (update, shutdown)
+- `run.yml` — main playbook; `playbooks/` — utilities (update.yml)
 - `roles/` — custom roles; external roles come from `requirements.yml`
 
 ## Usage