Global instructions.md AGENTS.md CLAUDE.md documentation clarification

### Describe the feature or problem you'd like to solve

Provide clear documentation about default behavior of Global instruction md files utilization

### Proposed solution

Provide clear documentation about default behavior of Global instruction md files utilization

This will avoid confusion for end users

There is currently some documentation around this (https://docs.github.com/en/copilot/how-tos/copilot-cli/customize-copilot/add-custom-instructions#agent-instructions) although seems to be slightly unclear/inaccurate in comparison to observed behavior of CLI

example (running on Windows os, WSL Ubuntu):
running `/env`:

however, I only have AGENTS.md in ~/.agents and CLAUDE.md in ~/.claude

_additionally for the above, a nice enhancement with respect to release notes of version 1.0.26 - 2026-04-14 "Avoid sending duplicate custom instruction files (e.g. copilot-instructions.md and CLAUDE.md with identical content) to reduce wasted tokens per turn", it would be nice here on the `/env` to demark as "(duplicate)" label suffix or something equivalent there to alleviate user concerns that these may bloat context/instructions sent and that they are properly being de-duplicated by copilot harness_

### Example prompts or workflows

_No response_

### Additional context

_No response_

Commencez par comparer la sortie observée de /env avec la documentation liée sur les instructions d’agent de GitHub Copilot CLI et déterminez le comportement de découverte par défaut pour les fichiers d’instructions globaux. C’est terminé lorsque la documentation explique précisément quels fichiers sont utilisés et comment les instructions en double sont gérées, notamment si /env indique une déduplication.

Rédigé par le modèle d'indexation à partir du texte de l'issue.