docs: add gstack section to CLAUDE.md

Use /browse for all web browsing, lists available gstack skills.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

CLAUDE.md

@@ -437,6 +437,14 @@ When a feature, fix, or significant piece of work is finished and merged/committ
 
 ---
 
+## gstack
+
+Use `/browse` from gstack for **all web browsing** — never use `mcp__claude-in-chrome__*` tools.
+
+**Available skills:** `/office-hours`, `/plan-ceo-review`, `/plan-eng-review`, `/plan-design-review`, `/design-consultation`, `/review`, `/ship`, `/browse`, `/qa`, `/qa-only`, `/design-review`, `/setup-browser-cookies`, `/retro`, `/investigate`, `/document-release`, `/codex`, `/careful`, `/freeze`, `/guard`, `/unfreeze`, `/gstack-upgrade`
+
+---
+
 ## Future Roadmap
 
 - **Phase 3:** PSA integrations (ConnectWise in progress), file attachments, client context, analytics