chore: add changeset for GitHub Copilot adapter

Author: cleberhensel

.changeset/github-copilot-adapter.md

@@ -0,0 +1,12 @@
+---
+"vibe-devtools": minor
+---
+
+Add GitHub Copilot adapter support
+
+- Implement CopilotAdapter for GitHub Copilot integration
+- Auto-detect GitHub Copilot installation via VSCode extensions
+- Generate `.github/copilot-instructions.md` with vibe commands and rules
+- Enable Copilot to understand and use vibe commands in projects
+- Full compatibility with existing Cursor, Gemini, and Claude adapters
+