UX fixes for item support drawer

One fix was that `position: absolute` stuff was appearing over the drawer, including the item search clear button, oof!

Another fix was for a weird bug(?) in Apollo Client, see comments

src/app/WardrobePage/index.js

@@ -44,7 +44,16 @@ function WardrobePage() {
   }, [error, toast]);
 
   return (
-    <Box position="absolute" top="0" bottom="0" left="0" right="0">
+    <Box
+      position="absolute"
+      top="0"
+      bottom="0"
+      left="0"
+      right="0"
+      // Create a stacking context, so that our drawers and modals don't fight
+      // with the z-indexes in here!
+      zIndex="0"
+    >
       <Grid
         templateAreas={{
           base: `"previewAndControls"

src/app/WardrobePage/support/ItemSupportDrawer.js

@@ -86,7 +86,18 @@ function SpecialColorFields({ item }) {
         }
       }
     `,
-    { variables: { itemId: item.id } }
+    {
+      variables: { itemId: item.id },
+
+      // HACK: I think it's a bug in @apollo/client 3.1.1 that, if the
+      //     optimistic response sets `manualSpecialColor` to null, the query
+      //     doesn't update, even though its cache has updated :/
+      //
+      //     This cheap trick of changing the display name every re-render
+      //     persuades Apollo that this is a different query, so it re-checks
+      //     its cache and finds the empty `manualSpecialColor`. Weird!
+      displayName: `ItemSupportDrawerManualSpecialColor-${new Date()}`,
+    }
   );
 
   const {