blocks that draw whatever the page is about

`/collections/amadoras-mythology` and `/collections/70s` are the same page with a different subject.
Building each would be absurd; hard-coding the arrangement would put it out of reach of the admin. So
the arrangement is built once — a template page, composed exactly like any other — and every
collection is drawn through it.

Four blocks read the subject: its name, its description, its specs, its photographs. They hold nothing
at all, not even a reference. `collections` holds no content because the list is a query; these hold
none because the subject is the URL, and the same block draws a different collection on the next
request.

Offered only on a template, and HIDDEN rather than disabled elsewhere. A greyed-out row invites "why
not here", and the answer — this page has no subject — is not something a tooltip fixes. Available and
silently drawing nothing is the worse failure.

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

web/usePages.ts

@@ -11,6 +11,14 @@ export type Page = {
   menu_label: string | null;
   position: number;
   is_home: boolean;
+  /**
+   * The arrangement a whole CLASS of pages is drawn with, rather than a page anybody visits.
+   *
+   * `collection` is the one today: every `/collections/<slug>` is drawn through it. Listed beside the
+   * pages because it is built exactly like one — a separate section for a single row would be a second
+   * place to learn — and marked so nothing offers to rename it, reorder it or put it in a menu.
+   */
+  is_template?: boolean;
 };
 
 /**