Collabs, as a third configuration of one panel

The same object as a collection and a gallery piece, so it is a config in
subjects.ts and a one-line panel — no new screen.

Two differences, both deliberate. It has no SPECS: a collab is a project rather
than an object, so there is no measurement or raw material and the form is a
name, an address and a description. And its title column is `project_name`,
which is the client's word and stays — the site's API publishes both that and
`title` so this panel reads one field like every other section, and the
translation lives in one router rather than as a branch in every screen.

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

web/sections/AddComponentDialog.tsx

@@ -31,6 +31,7 @@ export type ComponentKind =
   | 'partners'
   | 'collections'
   | 'pieces'
+  | 'collabs'
   | 'subject-cover'
   | 'subject-title'
   | 'subject-description'
@@ -93,6 +94,7 @@ export const CHOICES: Choice[] = [
   { kind: 'partners', label: 'Partners', hint: 'The partner logos, from Site', Icon: Handshake },
   { kind: 'collections', label: 'Collections', hint: 'Every collection, as a grid', Icon: LayoutGrid },
   { kind: 'pieces', label: 'Pieces', hint: 'Every gallery piece, as a grid', Icon: LayoutGrid },
+  { kind: 'collabs', label: 'Collabs', hint: 'Every collaboration, as a grid', Icon: LayoutGrid },
 
   /*
     The five that draw whatever the page is ABOUT, on a template.