foundation: fix mojibake in artist commentaries.

Fix certain artist commentaries for foundation.app containing scrambled
characters. Apparently caused by the Nokogiri HTML5 parser not handling
UTF-8 input correctly when the encoding isn't explicitly set to UTF-8.

app/logical/danbooru/http/html_adapter.rb

@@ -5,7 +5,8 @@ module Danbooru
       HTTP::MimeType.register_alias "text/html", :html
 
       def decode(str)
-        Nokogiri::HTML5(str, max_tree_depth: -1)
+        # XXX technically should use the charset from the http headers.
+        Nokogiri::HTML5.parse(str.force_encoding("utf-8"), max_tree_depth: -1)
       end
     end
   end

test/unit/sources/foundation_test.rb

@@ -61,5 +61,29 @@ module Sources
         assert_equal(image, case2.image_url)
       end
     end
+
+    should "parse UTF-8 commentaries correctly" do
+      source = Sources::Strategies.find("https://foundation.app/@SimaEnaga/~/107338")
+
+      assert_equal(<<~EOS, source.dtext_artist_commentary_desc)
+        【須佐之男尊/Susanoo-no-Mikoto】
+        He is the youngest child of the three brothers and has older sister "Amaterasu" and older brother "Tsukuyomi". They are children whose father is "Izanagi" and mother is "Izanami".They live in the Land of gods known as "Takamagahara".
+        He carried out a number of violence and caused trouble to people.
+        As a result, he was expelled from Takamagahara and moved to the human world.
+
+        【Meaning】
+        There is a theory that "須佐/susa" is a word
+        that means "凄まじい/susamajii (tremendous)" in Japanese.
+        ”之/no” is  a conjunction "of".
+        “男/o” means ”male”.
+        ”尊/mikoto” is a word that after the name of a god or a noble (Lord; Highness).
+        Colloquially, "The crazy guy." lol
+
+        【Concept】
+        He carries the bronze sword “Kusanagi-no Tsurugi”. This is one of the "three sacred treasures" and is the most famous sword in Japan. “Kusanagi-no Tsurugi” is dedicated to Atsuta Shrine in Aichi Prefecture, Japan.
+        The sword  is now sealed and no one has seen it.
+
+      EOS
+    end
   end
 end