Add Terminalbox Codex Remote SSH skill

[dieteradant]

What changed

Adds one external skill entry under Development & Code Tools for
configure-codex-remote-ssh.

Why

OpenAI Codex supports Remote SSH, but a safe connection workflow still has several sharp edges:
host-key verification, private-key handling, preserving existing SSH configuration, and ensuring
that codex is available through the remote login shell. This skill turns those checks into a
bounded, inspectable workflow for paid Terminalbox panes.

User impact

Readers get a one-command install path for a skill that:

• verifies the published ED25519 host fingerprint;
• never reads or uploads private-key contents;
• requires approval before changing SSH configuration;
• tests both SSH access and the remote Codex login shell; and
• states that Terminalbox hosting is paid and OpenAI access is separate.

Validation

• The linked public skill source returns HTTP 200.
• npx skills add Anchras/terminalbox-tools --list --full-depth discovers the skill.
• A clean isolated Codex install completed and matched the published SKILL.md byte-for-byte.
• The skill passes the Agent Skills structural validator.
• The README change is one line and passes git diff --check.