fix: unwrap PreviewOperationError cause in timeline failure messages

The refactored finalizeControlAction was recording the generic
PreviewOperationError.message (e.g. 'Desktop preview operation failed:
click.Input.dispatchMouseEvent (tab ...)') instead of the underlying
cause's message. Restore the cause-unwrapping logic so the timeline
captures the specific CDP/system error from PreviewOperationError.cause.

Author: cursoragent

apps/desktop/src/preview/Manager.ts

@@ -851,11 +851,13 @@ const makeNativeOperations = Effect.fn("PreviewManager.makeOperations")(function
       } else {
         const error = Option.getOrNull(Cause.findErrorOption(exit.cause));
         const interrupted = isPreviewAutomationControlInterruptedError(error);
+        const underlying =
+          isPreviewOperationError(error) && error.cause instanceof Error ? error.cause : error;
         yield* replaceAction(tabId, {
           ...actionEvent,
           status: interrupted ? "interrupted" : "failed",
           completedAt,
-          error: error instanceof Error ? error.message : String(error),
+          error: underlying instanceof Error ? underlying.message : String(underlying),
         });
       }
       const tabs = yield* SynchronizedRef.get(tabsRef);
@@ -2520,6 +2522,7 @@ export const PreviewManagerError = Schema.Union([
 export type PreviewManagerError = typeof PreviewManagerError.Type;
 
 export const isPreviewManagerError = Schema.is(PreviewManagerError);
+export const isPreviewOperationError = Schema.is(PreviewOperationError);
 export const isPreviewAutomationControlInterruptedError = Schema.is(
   PreviewAutomationControlInterruptedError,
 );