外部タグを分離 (#419) (#420)

**本番 DB のバックアップをかならずすること**

Reviewed-on: #420
Co-authored-by: miteruzo <miteruzo@naver.com>

backend/app/representations/post_repr.rb

@@ -87,15 +87,24 @@ module PostRepr
   end
 
   def tag_json post
-    post
+    internal_tags =
+        post
         .post_tags
         .reject { _1.tag.deprecated? }
         .sort_by { _1.tag.name }
-        .map do |post_tag|
-      TagRepr.inline(post_tag.tag).merge(
-          'children' => [],
-          'sections' => post_tag.sections.as_json(only: [:begin_ms, :end_ms]))
-    end
+        .map { |post_tag|
+          TagRepr.inline(post_tag.tag).merge(
+              'children' => [],
+              'sections' => post_tag.sections.as_json(only: [:begin_ms, :end_ms]))
+        }
+
+    external_tags =
+        post
+        .external_tags
+        .sort_by { _1.name }
+        .map { ExternalTagRepr.base(_1).merge('children' => [], 'sections' => []) }
+
+    internal_tags + external_tags
   end
 
   def thumbnail_url post, host: nil