test: fix flaky MainWindowTest.ModeBarLoadsAndModeChange (show window first)

This test failed intermittently on CI (Xvfb) with:
  Value of: window->m_modeBarShell->isHidden()  Actual: true  Expected: false

The fixture constructs MainWindow but never show()s it. QToolBar::isHidden()
reflects effective visibility, which is only realized once the parent window is
mapped — so under Xvfb the shell reports hidden and the assertion is racy. It hit
BOTH this branch and the unrelated CI-only PR #756 (which has no source changes),
confirming it's a pre-existing flake, not a regression.

Fix: show() the window and processEvents() before the visibility assertion.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

Author: fernandotonon

src/mainwindow_test.cpp

@@ -282,6 +282,13 @@ TEST_F(MainWindowTest, ModeBarLoadsAndModeChangeUpdatesStatusIndicator)
     ASSERT_EQ(window->m_modeBar->status(), QQuickWidget::Ready);
     EXPECT_GE(window->m_modeBar->minimumWidth(), 560);
     EXPECT_EQ(window->toolBarArea(window->m_modeBarShell), Qt::TopToolBarArea);
+    // QToolBar::isHidden() reflects effective visibility, which is only
+    // meaningful once the parent window has been shown. The fixture constructs
+    // MainWindow without show()ing it, so under Xvfb this assertion was flaky
+    // (the shell reports hidden until the window is mapped). Show the window and
+    // drain events so the toolbar's visibility is realized before asserting.
+    window->show();
+    app->processEvents();
     EXPECT_FALSE(window->m_modeBarShell->isHidden());
     ASSERT_NE(window->m_editModeLabel, nullptr);