Fix theme switcher preload scrim race

test/shell.d/background-test.sh

@@ -0,0 +1,13 @@
+#!/bin/bash
+source "$(dirname "$0")/base-test.sh"
+
+run_node_test <<'JS'
+const fs = require('fs')
+
+const backgroundQml = fs.readFileSync(path.join(root, 'shell/plugins/background/Background.qml'), 'utf8')
+
+assert(
+  /theme=\$\(omarchy-theme-switcher\); \[\[ -n \$theme \]\] && omarchy-theme-set \\"\$theme\\" >\/dev\/null 2>&1 &/.test(backgroundQml),
+  'background theme switcher starts theme application asynchronously after selection'
+)
+JS