fix: use portable shebang in shell scripts

Change #!/bin/bash to #!/usr/bin/env bash for better portability
on systems like NixOS where /bin/bash doesn't exist.

Fixes #910

packages/coding-agent/examples/extensions/doom-overlay/doom/build.sh

@@ -1,4 +1,4 @@
-#!/bin/bash
+#!/usr/bin/env bash
 # Build DOOM for pi-doom using doomgeneric and Emscripten
 
 set -e