Let a single column sit in a section and give buttons an alignment

A column may now live directly in a section, not only in a row - the way
to centre or narrow a button or a short text without a one-column row.
The align design token applies to buttons; because a button is
inline-flex, auto margins never centred it, so site.css turns an aligned
button into a fit-content block per device. The Drews seed uses the
token for its centred buttons.

Co-Authored-By: Claude Fable 5.1 <noreply@anthropic.com>

public/assets/editor-model.js

@@ -55,8 +55,12 @@ export const isContainer = block => ['section', 'row', 'column', 'gallery', 'log
 
 /** Containers that take one kind of child and nothing else. */
 export const ALLOW = { row: ['column'], gallery: ['image'], logos: ['image'], accordion: ['accordionitem'], tabs: ['tabitem'] };
-/** Blocks that exist only inside one of these parents. */
-export const REQUIRE = { column: ['row'], accordionitem: ['accordion'], tabitem: ['tabs'] };
+/**
+ * Blocks that exist only inside one of these parents. A column belongs to a row - and, as a
+ * single one, directly to a section: that is how a button or a short text gets centred and
+ * narrowed without a one-column row around it. Umut asked for exactly that.
+ */
+export const REQUIRE = { column: ['row', 'section'], accordionitem: ['accordion'], tabitem: ['tabs'] };
 /**
  * A row is not refused by any particular parent - a tab panel or an accordion entry may well
  * hold one - but it is not a thing a document starts with. At the top level a page begins with