finish the carousel rename in the panels

Two of these were live: PageBuilderPanel still compared kind === 'gallery' in
two places, so a carousel block's editor and its Choose button were both dead
branches. The type checker could not see them — both compare against string.

The rest is copy somebody reads: "Change gallery", "Name a new gallery",
"Reading the gallery", "Add to this gallery", Home's Gallery heading, and the
"Create Gallery" file action, now "Carousel from folder".

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

web/sections/AddComponentDialog.tsx

@@ -63,7 +63,7 @@ type Choice = {
  *
  * Named rather than omitted, and the ones named are things the site already HAS — media, video and
  * carousels all exist as concepts here. That is the difference between saying what is coming and
- * inventing a roadmap. Gallery stopped being one of them on 2026-08-31: the set, its ordering and the
+ * inventing a roadmap. The carousel stopped being one of them on 2026-08-31: the set, its ordering and
  * carousel that draws it were all already built, so the block is a reference to one.
  */
 export const CHOICES: Choice[] = [
@@ -73,7 +73,7 @@ export const CHOICES: Choice[] = [
 
     Image and Video were two rows — one of them greyed out as `soon` — and the distinction was never
     the editor's to make: the path names a real file and what that file IS is a fact about it. So the
-    picker asks for a file and the site works out the rest, which is also what a gallery item has
+    picker asks for a file and the site works out the rest, which is also what a carousel item has
     always done.
   */
   { kind: 'media', label: 'Media', hint: 'A photograph or a video, from the media store', Icon: Image },
@@ -104,11 +104,11 @@ export const CHOICES: Choice[] = [
     "it" for that reason. What differs between the sections is a path and a few spec labels, and both
     travel with the subject.
   */
-  { kind: 'subject-cover', label: 'Its lead photograph', hint: 'The first in its gallery, large', Icon: Image },
+  { kind: 'subject-cover', label: 'Its lead photograph', hint: 'The first in its carousel, large', Icon: Image },
   { kind: 'subject-title', label: 'Its name', hint: 'What this page is about', Icon: Heading },
   { kind: 'subject-description', label: 'Its description', hint: 'What was written about it', Icon: Type },
   { kind: 'subject-specs', label: 'Its specs', hint: 'Measurement, material, colours, and the rest', Icon: Ruler },
-  { kind: 'subject-carousel', label: 'Its photographs', hint: 'The gallery it points at', Icon: Images },
+  { kind: 'subject-carousel', label: 'Its photographs', hint: 'The carousel it points at', Icon: Images },
 ];
 
 export const AddComponentDialog = ({