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>

server/phy-z-dmz-sftp01/README.md

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+# phy-z-dmz-sftp01
+
+SFTP server in the DMZ for file exchange with external partners.
+
+| | |
+| - | - |
+| IP | 192.168.66.68 |
+| Ansible group | `phy_z_dmz_sftp01` |
+| Status | configured |
+
+## Services
+
+- SFTP access for external users
+- SSH password authentication is disabled (key-only), see `ansible/group_vars/phy_z_dmz_sftp01.yml`
+
+## Runbooks
+
+- [Add a new SFTP user](manuals/20260204-add-new-user.md)

server/phy-z-srv-cloud/README.md

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+# phy-z-srv-cloud
+
+Nextcloud server (`cloud.phytron.de`) for file sync and sharing.
+
+| | |
+| - | - |
+| IP | 192.168.66.66 |
+| Ansible group | `phy_z_srv_cloud` |
+| Status | configured |
+
+## Services
+
+- Nextcloud on Apache/MySQL/PHP 8.2, deployed via the `nextcloud` Ansible role
+- Mail (SMTP) configured via the `smtp_nextcloud` role (`--tags mail`)
+
+## Runbooks
+
+none yet

server/phy-z-srv-git/README.md

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+# phy-z-srv-git
+
+Git hosting server for internal repositories.
+
+| | |
+| - | - |
+| IP | 192.168.66.67 |
+| Ansible group | `phy_z_srv_git` |
+| Status | configured |
+
+## Services
+
+<!-- TODO: git service (software, version), install method, backup -->
+
+## Runbooks
+
+none yet

server/phy-z-srv-gpu01/README.md

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+# phy-z-srv-gpu01
+
+GPU server for AI/ML workloads. Hardware is ordered/assessed; OS setup and configuration are the next step.
+
+| | |
+| - | - |
+| IP | 192.168.66.69 (planned) |
+| Ansible group | `phy_z_srv_gpu01` |
+| Status | planned — not yet configured |
+
+## Hardware
+
+HPE ProLiant DL380 Gen12, 2× Intel Xeon 6714P (8-core, 4.0 GHz), 128 GB RAM,
+NVIDIA RTX PRO 6000 96 GB, 2× 960 GB NVMe SSD, redundant PSU — full BOM in [HW.md](HW.md).
+
+## Documents
+
+- [Hardware assessment (2026-07-06)](20260706-hardware-assessment.md)
+- [Software assessment (2026-07-06)](20260706-software-assessment.md)
+- [Deep dive (2026-07-07)](20260707-deep-dive.md)
+
+## Runbooks
+
+none yet

server/phy-z-srv-jira/README.md

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+# phy-z-srv-jira
+
+Atlassian Jira server for project and issue tracking.
+
+| | |
+| - | - |
+| IP | 192.168.66.41 |
+| Ansible group | `phy_z_srv_jira` |
+| Status | configured |
+
+## Services
+
+<!-- TODO: Jira version, install method, database, backup -->
+
+## Runbooks
+
+none yet