Support all AI agents via open Agent Skills format

[achandmsft]

Makes the existing Claude on Foundry skill work natively across all AI coding agents (GitHub Copilot, Claude Code, OpenAI Codex, Cursor, Gemini CLI, Amp, Goose, Junie, Qodo, Letta) by adopting the open Agent Skills format -- matching the pattern used by Azure-Samples/azure-openai-to-responses and microsoft/openclaw-dev.

Why

The repo already ships a strong skill at .github/skills/claude-on-foundry/SKILL.md, but only GitHub Copilot picks it up automatically. Non-Copilot agents (Claude Code, Codex, Cursor, Gemini CLI, Amp, Goose, etc.) look for AGENTS.md at the repo root and for skills/<name>/SKILL.md at the canonical Agent Skills path. They also rely on .github/agents/<name>.agent.md for the npx skills add owner/repo installer.

Changes

1. Move .github/skills/claude-on-foundry/SKILL.md -> skills/claude-on-foundry/SKILL.md (git rename, history preserved). This is the path the Agent Skills CLI and other agents look for.
2. Add .github/agents/claude-on-foundry.agent.md -- the Agent Skills manifest with YAML frontmatter (description, tools, argument-hint) that npx skills add Azure-Samples/claude reads.
3. Add AGENTS.md at the repo root -- the universal pointer file every non-Copilot agent reads. Restates the non-negotiable rules from copilot-instructions.md inline so they're available without an extra hop.
4. Update README "Ask Copilot" section -> "Ask your AI agent", adds the npx skills add Azure-Samples/claude one-liner and names the supported agents.

What this enables

�ash npx skills add Azure-Samples/claude

...then in any compatible agent:

Deploy Claude haiku to eastus2 with 50 TPM

The agent loads skills/claude-on-foundry/SKILL.md and drives this repo's own scripts and env-var contract instead of guessing.

What didn't change

• Skill body content (same playbook, same DIAGNOSE table, same destructive-action policy).
• .github/copilot-instructions.md content -- only the relative paths to the moved skill were updated.
• Bicep / Terraform IaC, scripts, src/ samples -- untouched.

Test

• git log --follow on the moved SKILL.md preserves history.
• The new manifest validates against the Agent Skills frontmatter schema used by the two reference repos.
• All in-repo links to the skill resolve to the new path (verified via grep).