Add support to copilot

[luisiul359]

This PR is for adding Microsoft Copilot as a supported harness, alongside the existing Claude Code plugin and Kiro Power.

• Install prompts added to README.md for the three interactive surfaces — VS Code, Copilot CLI, and Visual Studio — in the same paste-into-your-assistant style as the Claude Code and Kiro sections.
• copilot/mcp.json — a single canonical config carrying both top-level keys: servers (VS Code + Visual Studio) and mcpServers (Copilot CLI). One source of truth the install prompts copy the matching key out of.
• copilot/skills.md — the conventions doc, adapted from root SKILL.md and structured like the Kiro steering file (intro → Copilot First use / setup → full conventions body). Read automatically by VS Code, Visual Studio, the CLI (which also honors AGENTS.md), and the cloud agent.

[david-santos-os]

Reviewed with focus on two things: (a) parity of copilot/skill.md with the existing Claude Code / Kiro / root skill docs, and (b) whether the README changes affect the docs for the existing harnesses.

Overall: solid addition. I diffed copilot/skill.md section-by-section against the other three skill docs: every shared section (intro, Tools at a glance, Caveats, Rules, Names, Answering, Mentor session round-trip, Context Service visibility, Workflows) is byte-identical, with only the harness-specific First use / setup and Authenticating sections diverging — exactly the intended shape. The README additions are pure insertions and the existing harness sections are untouched. The dual-key canonical copilot/mcp.json, with comments explaining which surface reads which key, is a nice single-source-of-truth touch.

Five pre-merge asks, each as an inline comment:

1. Update CLAUDE.md + CONTRIBUTING.md for the fourth lockstep doc — the most important one (anchored on copilot/skill.md because those files aren't in this diff).
2. Restore an updated "harnesses we test against" sentence in the README.
3. Add the missing "retry the user's original request" step to the Copilot setup flow.
4. MINOR version bump per the CONTRIBUTING.md policy (anchored on the README because .claude-plugin/* isn't in this diff).
5. A sweep of small nits (fence typo, step-4 wording, VS auth path, casing, trailing newline, stale PR description).

One thing I couldn't validate locally: the Copilot CLI syntax (copilot mcp add --transport http, /mcp reload, /mcp show) and the Visual Studio "Manage Authentication" CodeLens. GitHub iterates these surfaces quickly, so a quick confirmation in the PR that each of the three flows was run end-to-end on current versions would be great.