chore: add .gstack/ to .gitignore

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

Author: justin808

.gitignore

@@ -101,3 +101,4 @@ packages/**/node_modules/
 junit.xml
 .lycheecache
 .playwright-cli/
+.gstack/