Fix rive_native setup script path in macOS Podfile

Ensures the rive_native setup script runs from the project root by setting PROJECT_ROOT and changing directory, allowing pubspec.yaml to be found in CI environments.

{{cookiecutter.out_dir}}/macos/Podfile

@@ -37,7 +37,20 @@ target 'Runner' do
 end
 
 post_install do |installer|
+  # Ensure rive_native's setup script runs from the project root so pubspec.yaml is found in CI.
   installer.pods_project.targets.each do |target|
     flutter_additional_macos_build_settings(target)
+    next unless target.name == 'rive_native'
+
+    target.shell_script_build_phases.each do |phase|
+      script = phase.shell_script
+      next unless script&.include?('rive_native:setup')
+      next if script.include?('PROJECT_ROOT="${SRCROOT}/../.."')
+
+      phase.shell_script = script.sub(
+        "set -e\n",
+        "set -e\nPROJECT_ROOT=\"${SRCROOT}/../..\"\ncd \"$PROJECT_ROOT\"\n"
+      )
+    end
   end
 end