Add GitHub Copilot provider adapter

## Goal Add GitHub Copilot as a Lineage provider target. ## Why GitHub Copilot remains one of the most widely adopted AI coding tools. Lineage should decide what a safe package activation story looks like for Copilot-centered workflows. ## Scope - Define whether Copilot support is local editor configuration, GitHub workflow integration, CLI integration, or a documented non-goal for V0. - Identify which package assets can be materialized safely for Copilot users. - Avoid requiring GitHub account tokens or provider auth state in packages. - Add inspect output that distinguishes supported behavior from user-managed Copilot setup. ## Acceptance Criteria - Copilot support has an explicit adapter decision. - Any local files Lineage writes are permission-gated and tested. - No GitHub/Copilot credentials are packaged. - Docs explain the supported flow and limitations.