Update theme_color_tags helper for new theme infrastructure (#37519)

app/helpers/theme_helper.rb

@@ -28,14 +28,17 @@ module ThemeHelper
     end
   end
 
-  def theme_color_tags(theme)
-    if theme == 'system'
+  def theme_color_tags(color_scheme)
+    case color_scheme
+    when 'auto'
       ''.html_safe.tap do |tags|
         tags << tag.meta(name: 'theme-color', content: Themes::THEME_COLORS[:dark], media: '(prefers-color-scheme: dark)')
         tags << tag.meta(name: 'theme-color', content: Themes::THEME_COLORS[:light], media: '(prefers-color-scheme: light)')
       end
-    else
-      tag.meta name: 'theme-color', content: theme_color_for(theme)
+    when 'light'
+      tag.meta name: 'theme-color', content: Themes::THEME_COLORS[:light]
+    when 'dark'
+      tag.meta name: 'theme-color', content: Themes::THEME_COLORS[:dark]
     end
   end
 
@@ -65,8 +68,4 @@ module ThemeHelper
       Setting.custom_css&.then { |content| Digest::SHA256.hexdigest(content) }
     end
   end
-
-  def theme_color_for(theme)
-    theme == 'mastodon-light' ? Themes::THEME_COLORS[:light] : Themes::THEME_COLORS[:dark]
-  end
 end

app/views/layouts/application.html.haml

@@ -21,7 +21,7 @@
       %link{ rel: 'mask-icon', href: frontend_asset_path('images/logo-symbol-icon.svg'), color: '#6364FF' }/
     %link{ rel: 'manifest', href: manifest_path(format: :json) }/
     = javascript_inline_tag 'theme-selection.js'
-    = theme_color_tags current_theme
+    = theme_color_tags color_scheme
     %meta{ name: 'mobile-web-app-capable', content: 'yes' }/
 
     %title= html_title