Show related packages based on description embeddings

Package pages get a "Related packages" section: a nearest neighbor
query against the package's own stored embedding (no external service
call), excluding the package itself. Packages without an embedding
render no section.

app/controllers/packages_controller.rb

@@ -30,6 +30,9 @@ class PackagesController < ApplicationController
       @screenshots = @package.screenshots.accessible_by(current_ability, :view).paginate(
         page: @page, per_page: 6
       )
+      # Semantic recommendations based on the package's own description
+      # embedding - a plain nearest neighbor query, no service call.
+      @related_packages = @package.related_packages
     end
   end