chore: add copilot instructions to gitignore

Author: danieltruong

.gitignore

@@ -57,3 +57,7 @@ convert-scss-vars-to-css-vars.sh
 convert-slash-comments.sh
 migrate-scss-to-css.sh
 claude.md
+
+# Internal AI assistant notes
+.github/copilot-instructions.md
+.github/instructions/