fix(commandline): prevent false theme apply during perview (@byseif21) (monkeytypegame#6930)

* When leaving a theme item to a non‑theme item inside the mixed
commandline list, the preview theme temporarily applied after closing
the commandline without selecting it. so switched back to clearPreview()
as it was,
#### to REPRODUCE: type e.g "theme off" in the commandline then close
the commandline.

* and to fix the preview flashing issue that the false was added for, in
custom themes included setCustomThemeId with changeTheme in the check ,
so custom theme hovers are now treated as the same preview context and
no longer clear the preview between items.

Author: byseif21

frontend/src/ts/commandline/commandline.ts

@@ -564,10 +564,13 @@ async function updateActiveCommand(): Promise<void> {
   keepActiveCommandInView();
 
   clearFontPreview();
-  if (/changeTheme.+/gi.test(command.id)) {
+  if (
+    command.id?.startsWith("changeTheme") ||
+    command.id?.startsWith("setCustomThemeId")
+  ) {
     removeCommandlineBackground();
   } else {
-    void ThemeController.clearPreview(false);
+    void ThemeController.clearPreview();
     addCommandlineBackground();
   }