[Hackathon] Add GitHub Copilot as an `agent install` target

[Davidson3556]

Discord Username / User ID

Davidson

What does this improvement do?

Adds GitHub Copilot as an agent install target — the most widely-used AI coding assistant, currently the biggest gap in the target set (claude, codex, cursor, cline, antigravity, kiro, windsurf).

GitHub Copilot reads path-specific custom instructions from .github/instructions/*.instructions.md (VS Code, Visual Studio, and Copilot Chat), with YAML frontmatter carrying an applyTo glob. So the TestSprite verification-loop skill can be installed there the same way it is for Cursor/Cline/Windsurf.

Details / implementation notes

Proposal — a copilot own-file target:

• Path: .github/instructions/testsprite-verify.instructions.md (and testsprite-onboard.instructions.md alongside).
• Frontmatter: applyTo: '**' + description: <skill description> — attaches the guidance to every request in the repo. Copilot instruction files have no on-demand "model decides" mode (unlike Cursor's alwaysApply: false or Windsurf's trigger: model_decision), so always-apply is the correct idiom.
• Always-on ⇒ compact body: because applyTo: '**' means the file is injected into every Copilot request, the target renders the compact skill body (~6 KB) rather than the full ~23 KB body — the same reasoning behind windsurf's compact render, keeping the always-injected context cost small.

It slots into the existing TARGETS machinery, so agent list, setup --agent, and skill-nudge install-detection pick it up automatically.

Ref: GitHub Copilot custom instructions docs (.github/instructions/*.instructions.md, applyTo frontmatter).

Note on scope: I saw the earlier "target policy settled this round" note when windsurf/kiro/gemini were accepted. I'm proposing Copilot as the clear next-highest-value target and have a complete PR ready, but happy to defer if the target set is closed for now.

I have a PR ready for this.

Confirmations

• I have searched existing issues and this is not a duplicate.
• I have provided my Discord identity above for reward coordination.

[Davidson3556]

Closing in favor of #195, the hackathon-template refile of this same proposal (it carries the hackathon label and is assigned). PR #194 now references #195 (Fixes #195). Same content, no change to the implementation.