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/CarouselItems.tsx

@@ -8,15 +8,15 @@ import { readableError } from '../errors';
 import { thumbUrl } from '../thumbnail';
 
 /**
- * One gallery's contents: what is in it, in what order, and what each picture is called.
+ * One carousel's contents: what is in it, in what order, and what each picture is called.
  *
  * ── Why it is here and not a link to Carousels ──
  *
- * A gallery block on a page IS a gallery, and being sent to another section to reorder it means
+ * A carousel block on a page IS a carousel, and being sent to another section to reorder it means
  * losing the page you were arranging it for. The set is a thing of its own — that is why it has its
  * own section — but editing it is something you do while looking at where it appears.
  *
- * ── It reads the gallery itself ──
+ * ── It reads the carousel itself ──
  *
  * `GET /carousels/:id`, rather than being handed one. The block knows an id and nothing else, and a
  * component that fetches what it needs can be dropped anywhere something knows an id.
@@ -29,21 +29,21 @@ import { thumbUrl } from '../thumbnail';
  */
 
 type Item = { id: number; url: string; alt: string | null };
-type Gallery = { id: number; name: string; slug: string; items: Item[] };
+type Carousel = { id: number; name: string; slug: string; items: Item[] };
 
 export const CarouselItems = ({ carouselId, onChanged }: { carouselId: number; onChanged?: () => void }) => {
   const client = useClient();
   const clientRef = useRef(client);
   clientRef.current = client;
 
-  const [gallery, setCarousel] = useState<Gallery | null>(null);
+  const [carousel, setCarousel] = useState<Carousel | null>(null);
   const [busy, setBusy] = useState(false);
   const [error, setError] = useState<string | null>(null);
   const [picking, setPicking] = useState(false);
 
   const load = useCallback(async () => {
     try {
-      setCarousel((await clientRef.current.get<{ data: Gallery }>(`/fofos-admin/carousels/${carouselId}`)).data);
+      setCarousel((await clientRef.current.get<{ data: Carousel }>(`/fofos-admin/carousels/${carouselId}`)).data);
     } catch (failure) {
       setError(readableError(failure));
     }
@@ -60,7 +60,7 @@ export const CarouselItems = ({ carouselId, onChanged }: { carouselId: number; o
     try {
       await call();
       await load();
-      // The page draws this gallery, so it is now showing the old one.
+      // The page draws this carousel, so it is now showing the old one.
       onChanged?.();
     } catch (failure) {
       setError(readableError(failure));
@@ -83,19 +83,19 @@ export const CarouselItems = ({ carouselId, onChanged }: { carouselId: number; o
   const orderedRef = useRef<Item[] | null>(null);
 
   const moveOver = (event: React.DragEvent, overId: number) => {
-    if (dragged === null || !gallery) return;
+    if (dragged === null || !carousel) return;
     // Without this the drop is refused and the browser animates the row back to where it started.
     event.preventDefault();
     if (dragged === overId) return;
 
-    const next = [...gallery.items];
+    const next = [...carousel.items];
     const from = next.findIndex((one) => one.id === dragged);
     const to = next.findIndex((one) => one.id === overId);
     if (from < 0 || to < 0) return;
 
     next.splice(to, 0, next.splice(from, 1)[0]!);
     orderedRef.current = next;
-    setCarousel({ ...gallery, items: next });
+    setCarousel({ ...carousel, items: next });
   };
 
   const commitOrder = () => {
@@ -110,19 +110,19 @@ export const CarouselItems = ({ carouselId, onChanged }: { carouselId: number; o
     );
   };
 
-  if (!gallery) return <p className="text-xs text-muted-foreground">{error ?? 'Loading…'}</p>;
+  if (!carousel) return <p className="text-xs text-muted-foreground">{error ?? 'Loading…'}</p>;
 
   return (
     <div className="flex flex-col gap-2">
       <div className="flex items-baseline gap-2">
-        <span className="min-w-0 flex-1 truncate text-xs font-medium">{gallery.name}</span>
+        <span className="min-w-0 flex-1 truncate text-xs font-medium">{carousel.name}</span>
         <span className="shrink-0 text-[10px] text-muted-foreground">
-          {gallery.items.length} item{gallery.items.length === 1 ? '' : 's'}
+          {carousel.items.length} item{carousel.items.length === 1 ? '' : 's'}
         </span>
       </div>
 
       <ul className="flex flex-col gap-1">
-        {gallery.items.map((item) => (
+        {carousel.items.map((item) => (
           <li
             key={item.id}
             /* The row is the drop target; the grip is what drags. See the note on the handler. */
@@ -213,7 +213,7 @@ export const CarouselItems = ({ carouselId, onChanged }: { carouselId: number; o
           setPicking(false);
           void send(() => clientRef.current.post(`/fofos-admin/carousels/${carouselId}/items`, { urls: [url] }));
         }}
-        title="Add to this gallery"
+        title="Add to this carousel"
       />
     </div>
   );