Fix assertion type combo box height in TestStepDialog

Set minimum height (28px) on type combo box to display selection.

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

src/cmdforge/gui/dialogs/test_step_dialog.py

@@ -301,6 +301,7 @@ class TestStepDialog(QDialog):
 
         # Type dropdown
         type_combo = QComboBox()
+        type_combo.setMinimumHeight(28)
         for type_id, display_name, tooltip in self.ASSERTION_TYPES:
             type_combo.addItem(display_name, type_id)
             idx = type_combo.count() - 1