Fix generated Codex skill paths

[msr-hickory]

Summary

• switch generated Codex skill references from ~/.Codex/.Codex to lowercase ~/.codex/.codex paths for case-sensitive hosts
• restore intended Claude/Codex wording in generated cross-model review guidance

Verification

• rg -n --fixed-strings '~/.Codex' .agents/skills/gstack returned no matches from ai-config checkout
• rg -n --fixed-strings '.Codex/' .agents/skills/gstack returned no matches from ai-config checkout
• rg -n 'Codex and Codex|both Codex and Codex|Codex \+ Codex|Codex adversarial subagent' .agents/skills/gstack returned no matches from ai-config checkout

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[time-attack]

@16francej — recommend closing this PR as superseded by #1996. This branch changes generated outputs, removes a source template, and does not update generator source or behavior coverage; #1996 is the narrow source-level fix for the project-instruction path problem. Preserve the filename report and contributor attribution in #1996, while excluding global substitutions, unsupported paths, and template deletion.

[capy-ai]

Thanks for the PR, @msr-hickory. Closing this one: it edits generated SKILL.md output rather than the generator, and the source-level fix is #1996's CLAUDE.md→AGENTS.md path rewrite, already on main. Appreciate you taking the time.