chore(repo): untrack docs/ directory

Remove docs/plan/studio-phase-1.md from git tracking and add docs/ to .gitignore.

Author: quanru

.gitignore

@@ -138,6 +138,7 @@ packages/playground/static/
 tsconfig.build.tsbuildinfo
 .webx
 .mcp.json
+docs/
 package-lock.json
 packages/all-in-one-playground/static/*