fix: apply initial DOM state from preferences store on load (no-flash in browser dev mode)

src/lib/stores/preferences.svelte.js

@@ -100,6 +100,12 @@ function persistToSQLite(prefs) {
 
 let preferences = $state(readFromDOM());
 
+// Ensure data-theme and zone attributes are always present on the DOM, even
+// when there is no Tauri webview injection script (e.g. browser dev mode).
+if (typeof window !== 'undefined') {
+  applyToDOM(preferences);
+}
+
 export function getPreferences() {
   return preferences;
 }