Prevent long quoted excerpts from breaking layout in Notebook

Because of the sometimes-arcane nature of grid layouts, it is sometimes
necessary to apply definite width values on grid areas (versus `auto`)
to prevent content from escaping.

This fixes a situation in which very long unbroken quoted excerpts could
blow out the column width in the Notebook.

See https://css-tricks.com/preventing-a-grid-blowout/

src/styles/sidebar/components/NotebookView.scss

@@ -5,8 +5,10 @@
 .NotebookView {
   display: grid;
   row-gap: var.$layout-space--small;
+
   // See https://css-tricks.com/preventing-a-grid-blowout/
   grid-template-columns: minmax(0, auto);
+
   grid-template-areas:
     'heading'
     'filters'
@@ -43,6 +45,9 @@
       'filters results'
       'items items';
 
+    // See https://css-tricks.com/preventing-a-grid-blowout/
+    grid-template-columns: minmax(0, auto) minmax(0, auto);
+
     &__filters {
       justify-self: start;
     }