Clean up inventory, group_vars, and prefill READMEs

- hosts.ini: underscore group names, hostname aliases with ansible_host
- move ansible_user/ansible_port to group_vars/all.yml
- rename group_vars files to match underscore group names
- trim sftp group_vars to its only override (password auth off)
- run.yml: load moved secrets file (group_vars/secrets.yml)
- untrack .DS_Store, extend .gitignore
- prefill root/ansible/server READMEs, add jira + cloud server folders
- update CLAUDE.md to match

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

ansible/group_vars/all.yml

@@ -1,4 +1,8 @@
 ---
+# connection settings (identical for all hosts)
+ansible_user: sbxadmin
+ansible_port: 22
+
 # generic settings
 main_username: sbxadmin
 main_groupname: "{{ main_username }}"