pools: fix pool gallery page layout.

Fix the /pools/gallery page layout being broken by 8841de68a.

This required refactoring the PostGalleryComponent to take a set of
PostPreviewComponents instead of a set of Posts.

The upshot is that it's technically possible to have adjustable
thumbnail sizes on the pool gallery page now (although this is not yet
exposed in the UI).

app/helpers/components_helper.rb

@@ -3,13 +3,22 @@ module ComponentsHelper
     render PostPreviewComponent.new(post: post, **options)
   end
 
-  def post_previews_html(posts, **options)
+  # Render a set of posts as thumbnail gallery.
+  #
+  # @param posts [ActiveRecord::Relation<Post>, Array<Post>] A set of posts.
+  # @param options [Hash] A hash of options for the PostGalleryComponent and PostPreviewComponent.
+  def render_post_gallery(posts, **options, &block)
     posts = posts.includes(:media_asset) if posts.is_a?(ActiveRecord::Relation)
-    render PostPreviewComponent.with_collection(posts, **options)
-  end
 
-  def render_post_gallery(posts, current_user: CurrentUser.user, **options, &block)
-    render PostGalleryComponent.new(posts: posts, current_user: current_user, **options), &block
+    render(PostGalleryComponent.new(**options)) do |gallery|
+      posts.each do |post|
+        gallery.post(post: post, size: gallery.size, **options)
+      end
+
+      if block_given?
+        yield(gallery, posts)
+      end
+    end
   end
 
   def render_comment(comment, current_user:, **options)