feat(web): useSetVisibility hook + adjacentTransitions helper + MSW handler

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

web/src/api/queries.ts

@@ -199,3 +199,32 @@ export function useDeleteObject() {
     onSuccess: () => qc.invalidateQueries({ queryKey: ["objects"] }),
   });
 }
+
+type Visibility = "draft" | "internal" | "public";
+
+/** Error carrying the HTTP status so callers can branch 422-gate vs 409-illegal. */
+export class VisibilityError extends Error {
+  constructor(public status: number) {
+    super(`visibility change failed (${status})`);
+    this.name = "VisibilityError";
+  }
+}
+
+export function useSetVisibility() {
+  const qc = useQueryClient();
+
+  return useMutation({
+    mutationFn: async ({ id, visibility }: { id: string; visibility: Visibility }) => {
+      const { response } = await api.POST("/api/admin/objects/{id}/visibility", {
+        params: { path: { id } },
+        body: { visibility },
+      });
+
+      if (response.status !== 204) throw new VisibilityError(response.status);
+    },
+    onSuccess: (_result, { id }) => {
+      void qc.invalidateQueries({ queryKey: ["object", id] });
+      void qc.invalidateQueries({ queryKey: ["objects"] });
+    },
+  });
+}