Add dark mode payload to theme-update message

src/external_app/external_messaging.ts

@@ -111,6 +111,9 @@ interface EMOutgoingMessageExoplayerStop extends EMMessage {
 
 interface EMOutgoingMessageThemeUpdate extends EMMessage {
   type: "theme-update";
+  payload: {
+    darkMode: boolean;
+  };
 }
 
 interface EMOutgoingMessageHaptic extends EMMessage {

src/state/themes-mixin.ts

@@ -179,6 +179,11 @@ export default <T extends Constructor<HassBaseEl>>(superClass: T) =>
         themeMeta.setAttribute("content", themeColor);
       }
 
-      this.hass!.auth.external?.fireMessage({ type: "theme-update" });
+      this.hass!.auth.external?.fireMessage({
+        type: "theme-update",
+        payload: {
+          darkMode,
+        },
+      });
     }
   };