Pieces: the Gallery, as a section like Collections

The Gallery is a flat list of peças, each with a title, a gallery of mixed
media, and the specs from the client's sitemap — measurement, raw material,
colours, and NOTAS: production time and shipping conditions.

That is a collection one level flatter, so the panel is shared rather than
copied. SubjectPanel and SubjectFields take a section config (subjects.ts);
CollectionsPanel and PiecesPanel are one line each.

The five template blocks are renamed collection-* to subject-*. They never read
anything collection-specific, and copying them per section would have meant
twenty kinds by the time Drops and Collabs land.

Called Pieces in the nav, not Gallery — there is already a Galleries section
meaning a named set of media, and two rows called Gallery and Galleries is a
question somebody has to answer every time they look at it.

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

web/DetailPanel.tsx

@@ -6,6 +6,7 @@ import { sectionFor, sectionOpen, type SectionKey } from './sections';
 import { AdministrationPanel } from './AdministrationPanel';
 import { MediaPanel } from './MediaPanel';
 import { CollectionsPanel } from './sections/CollectionsPanel';
+import { PiecesPanel } from './sections/PiecesPanel';
 import { GalleriesPanel } from './sections/GalleriesPanel';
 import { LayoutPanel } from './sections/LayoutPanel';
 import { PageBuilderPanel } from './sections/PageBuilderPanel';
@@ -48,6 +49,7 @@ import { useReady } from './useReady';
 const PANELS: Partial<Record<SectionKey, () => React.JSX.Element>> = {
   layout: LayoutPanel,
   collections: CollectionsPanel,
+  pieces: PiecesPanel,
   galleries: GalleriesPanel,
   messages: MessagesPanel,
   administration: AdministrationPanel,