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/EditorPanel.tsx

@@ -37,7 +37,15 @@ export const EditorPanel = () => {
       </div>
 
       {editor ? (
-        <div className="min-h-0 flex-1 overflow-auto p-3">{editor}</div>
+        /*
+          `@container`, once, for every section inside it.
+
+          The sections lay out in two columns and have to fall back to one when the panel is dragged
+          narrow — and the window's width says nothing about that, because the width here is a divider
+          somebody moves. Declared on the scroller rather than per section, so a new section is
+          responsive by being in the column rather than by remembering to say so.
+        */
+        <div className="@container min-h-0 flex-1 overflow-auto p-3">{editor}</div>
       ) : (
         <div className="flex min-h-0 flex-1 items-center justify-center p-6 text-center">
           {/* Names what the panel is FOR rather than saying it is empty. "Nothing selected" describes