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_

Beginne damit, die beobachtete Ausgabe von /env mit der verlinkten Dokumentation zu den Agentenanweisungen von GitHub Copilot CLI zu vergleichen, und ermittle das standardmäßige Suchverhalten für globale Anweisungsdateien. Als abgeschlossen gilt die Aufgabe, wenn die Dokumentation genau erklärt, welche Dateien verwendet werden und wie doppelte Anweisungen behandelt werden, einschließlich der Frage, ob /env auf eine Deduplizierung hinweist.

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