Add AI coding assistant instructions and TypeScript skill

[janechu]

Pull Request

📖 Description

Adds agent-agnostic AI coding assistant instructions for the FAST monorepo. This uses the standard .github/copilot-instructions.md location that any AI coding assistant can consume.

What's included:

• .github/copilot-instructions.md — Top-level instructions covering repository overview, packages, key rules, TypeScript key rules, common commands, and an acceptance checklist with required CI gates (npm run build, npm run test, npm run format:check, npm run checkchange).
• .github/typescript/SKILL.md — Detailed TypeScript patterns and conventions for the FAST monorepo (Web Component authoring, templates, styles, observables, DI, testing conventions, module/export conventions).

👩‍💻 Reviewer Notes

• All instructions are now in .github/copilot-instructions.md using agent-agnostic language.
• The TypeScript skill file has no YAML frontmatter or agent-specific wording.
• The acceptance checklist is in copilot-instructions.md only (not duplicated in SKILL.md).

📑 Test Plan

• Verify .github/copilot-instructions.md is picked up by AI coding assistants (GitHub Copilot, Claude Code)
• Verify .github/typescript/SKILL.md contains detailed TypeScript patterns without agent-specific language
• Confirm no CLAUDE.md exists at the repo root

✅ Checklist

General

• I have included a change request file using $ npm run change
• I have tested my changes.
• I have updated the project documentation to reflect my changes.
• I have read the CONTRIBUTING documentation and followed the standards for this project.

⏭ Next Steps

• Add additional skill files under .github/<domain>/SKILL.md for other areas (e.g., testing, SSR) as needed.

🤖 Generated with Claude Code

[chrisdholt]

Do we need to be explicit to CLAUDE.md here or would Claude pickup either instructions or an Agents.md file?

[janechu]

Do we need to be explicit to CLAUDE.md here or would Claude pickup either instructions or an Agents.md file?

According to the GitHub docs it may just be for that agent, since I used claude to generate the instructions it created the CLAUDE.md file explicitly. I'm not sure how other agents will interact with an agent specific file, we may want to let them generate their own and then create a general AGENTS.md file. I think we could do both, this seems like a good starting point.

[janechu]

@chrisdholt I've updated to the non-agent specific copilot-instructions.md. I think simply using that as an entry point should be enough and we can subsequently just add more SKILLS.md as needed.

[radium-v]

this needs to be removed, or reversed to discourage using barrel exports