Revert "DEV: prioritize new email styles over existing, to make customization easier (#30244)" (#30297)

This reverts commit 9694dc6cb0.

Some of our previous email styling depended on this 'incorrect' ordering, so the change caused some text to become illegible. Reverting while we work out a better solution

lib/email/styles.rb

@@ -33,7 +33,7 @@ module Email
       existing = node["style"]
       if existing.present?
         # merge styles
-        node["style"] = "#{existing}; #{new_styles}"
+        node["style"] = "#{new_styles}; #{existing}"
       else
         node["style"] = new_styles
       end