.github/copilot-instructions.md redirects to AGENTS.md

User story

As a GitHub Copilot user (Chat, PR review, or the Copilot coding agent), I want .github/copilot-instructions.md to load automatically so that Copilot-generated code follows the same conventions as human- and agent-written code.

Why

GitHub Copilot reads .github/copilot-instructions.md for project-level guidance. Pointing it at AGENTS.md keeps everything in one place.

Acceptance criteria

• .github/copilot-instructions.md exists.
• Its body is a one-line redirect: See [AGENTS.md](../AGENTS.md) for repo conventions.
• Any Copilot-specific guidance (e.g., referencing .github/copilot/*.instructions.md files once they exist) is appended after the redirect.

Out of scope

• Creating the task-specific instruction/prompt files under .github/copilot/ (separate issue).

Notes

• Target release: none — chore
• Depends on AGENTS.md landing first.
• Source: modernization assessment §6.1.