[CHORE] adding agents.md (#3699)

* [CHORE] adding agents.md

Signed-off-by: Nicolas Takashi <nicolas.tcs@hotmail.com>

* Address review feedback: link naming conventions, note procfs usage

Signed-off-by: Nicolas Takashi <nicolas.takashi@dash0.com>

* Trim AGENTS.md per review: drop directory-listing sections, keep non-inferable rules

Signed-off-by: Nicolas Takashi <nicolas.takashi@dash0.com>

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Signed-off-by: Nicolas Takashi <nicolas.tcs@hotmail.com>
Signed-off-by: Nicolas Takashi <nicolas.takashi@dash0.com>