docs(ai): Add initial AI instruction files

[dmcilvaney]

Implement phase 1 of #15628

[Copilot]

Pull request overview

Adds initial agent-facing documentation and skill placeholders to support AI-assisted workflows in the Azure Linux repo (phase 1 of the AI repo tooling plan), including a root entrypoint guide and directory-specific guidance.

Changes:

• Introduces root and per-directory AGENTS.md guides (repo, components, distro config).
• Adds initial .github/copilot-instructions.md with repo layout, concepts, and CLI reference.
• Adds placeholder skill files for common tasks (azl-add-component, azl-build-component, azl-fix-overlay).

Reviewed changes

Copilot reviewed 7 out of 7 changed files in this pull request and generated 3 comments.

Show a summary per file

File	Description
AGENTS.md	Root agent guide linking to skills and directory-specific guidance.
base/comps/AGENTS.md	Component-management rules and links to relevant skills/schema.
distro/AGENTS.md	Distro config guidance and build-default pointers.
.github/copilot-instructions.md	Main Copilot instruction doc: layout, concepts, CLI reference, hygiene rules.
.github/skills/azl-add-component/SKILL.md	Placeholder skill definition for adding components.
.github/skills/azl-build-component/SKILL.md	Placeholder skill definition for building/debugging components.
.github/skills/azl-fix-overlay/SKILL.md	Placeholder skill definition for diagnosing overlay issues.

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[reubeno]

@dmcilvaney What feedback are you looking for? Are these really placeholders? And if so, does that mean corrections / clarifications aren't useful?

[dmcilvaney]

@dmcilvaney What feedback are you looking for? Are these really placeholders? And if so, does that mean corrections / clarifications aren't useful?

For the placeholders themselves, no, unless you have feedback on the meta structure. This is mostly just a foundational set of instructions which the nitty gritty stuff to follow. I just wanted to ensure there was 'something' in place when adding a reference to it.

[christopherco]