feat(media): align visual checks and variant UI with merged design

features/image_variants_screens.feature

@@ -330,12 +330,11 @@ Feature: Image variants settings screens, list and add/edit slide-over
       And its footer is 64 px high with "Cancel" and a primary "Add variant", and the status text is empty
       And focus moves to the Name field
 
-    Scenario: Add variant opens a full page on mobile
+    Scenario: Add variant opens a bottom sheet on mobile
       Given the viewport is below 640 px
       When the user activates "Add variant"
-      Then a full-screen page opens with a 56 px header holding an arrow-left back button and the title "Add variant", no x button
+      Then a tall bottom sheet opens as specified in features/variants_visual_conformance.feature, "Add variant is a tall bottom sheet on mobile", superseding the former full-page layout
       And the form is followed by the Preview section, stacked, separated by a top border
-      And the footer is 72 px high with "Cancel" and "Add variant" sharing the width
 
     Scenario: Edit opens with the stored values
       When the user chooses "Edit" on the row "hero"