Rename horizontalgallery block to horizontal-gallery

- Follow Kirby naming convention with dashes
- Update all references (blueprint, snippet, plugin registration)
- Rebuild plugin with new name

Co-Authored-By: Claude Sonnet 4.5 <noreply@anthropic.com>

site/blueprints/pages/report.yml

@@ -46,12 +46,12 @@ tabs:
               - "1/1"
               - "1/2, 1/2"
             fieldsets:
-              - text
               - heading
+              - text
               - image
-              - video
               - beforeafter
-              - horizontalgallery
+              - video
+              - horizontal-gallery
       - width: 1/6
         fields:
           emptyRight: