Revert "docs: recommend gstack for AI-assisted workflows (#11770)"

This reverts commit 8acdd53025.

CLAUDE.md

@@ -68,16 +68,3 @@ Before cutting a branch or opening a PR, run the base-green check (`AGENTS.md`
 "Base-green check"; project skills reference it as `.agents/skills/_shared/base-green.md`). A PR
 opened while the base tip is red must carry `⚠️ base-red inherited: #<issue>` in its body. To
 drain an accumulated red state (base tip + red PRs), use the `/sweep-reds` skill.
-
-## gstack (recommended)
-
-This project uses [gstack](https://github.com/garrytan/gstack) for AI-assisted workflows.
-Install it for the best experience:
-
-```bash
-git clone --depth 1 https://github.com/garrytan/gstack.git ~/.claude/skills/gstack
-cd ~/.claude/skills/gstack && ./setup --team
-```
-
-Skills like /qa, /ship, /review, /investigate, and /browse become available after install.
-Use /browse for all web browsing. Use ~/.claude/skills/gstack/... for gstack file paths.