Fix theme.json generation to handle :host selector in theme layer of …

…app.css

- Previously, wordpressThemeJson checked that themeContent starts with  `:root{`
- Tailwind outputs `:root, :host {`, causing an early return.
- Remove '{' and add trim() to support non-minified app.css.

resources/js/build/wordpress.js

@@ -206,7 +206,7 @@ export function wordpressThemeJson({
       }
 
       const themeContent = themeMatch[1]
-      if (!themeContent.startsWith(':root{')) {
+      if (!themeContent.trim().startsWith(':root')) {
         return;
       }