chore(devcontainer): add ast-grep (#14018)

ast-grep was missing in the dev container. But the AI was trying to use it.

Author: sapphi-red

.devcontainer/postCreateCommand.sh

@@ -8,4 +8,6 @@ curl -L --proto '=https' --tlsv1.2 -sSf https://raw.githubusercontent.com/cargo-
 
 npm i -g @withgraphite/graphite-cli
 
+cargo binstall ast-grep -y
+
 just init