an Alignment control beside Width

Left, Centred, Right on the selected block. Left writes nothing, so a block that
has never been touched inherits the page.

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

web/canvas.ts

@@ -57,6 +57,8 @@ export type CanvasComponent = {
   title?: string | null;
   /** `main`, `page` or null — how wide it is allowed to be. See the site's schema. */
   width?: string | null;
+  /** `center`, `right` or null — how the block's own content sits. See the site's schema. */
+  align?: string | null;
   /*
     One optional field per kind that the panel reads back. Not `Record<string, unknown>`: every reader
     would then need a cast, and the point of naming them is that the compiler knows `free-text` holds