the editor sections fall to one column when it is narrow

A container query on the scroller, once, so a new section is responsive by being
in the column rather than by remembering to say so. Below 320px the two-column
sections stack instead of truncating every select to "Martia…".

Colors stays flex-wrap: three swatches in a two-column grid is 2 and 1.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>

web/sections/FontSizesTab.tsx

@@ -60,7 +60,7 @@ export const FontSizesTab = ({
   };
 
   return (
-    <div className="grid grid-cols-2 gap-3">
+    <div className="grid grid-cols-1 gap-3 @[20rem]:grid-cols-2">
       {ROLES.map((role) => {
         const current = sizes[role.size];
         const own = current?.[key];