Merge commit '02ea16150647ac3baf0bb8a89203ccc7200b4a2f' into glitch-soc/merge-upstream

Conflicts:
- `app/lib/themes.rb`
- `app/views/layouts/application.html.haml`
- `app/views/layouts/embedded.html.haml`
- `app/views/layouts/error.html.haml`
- `config/settings.yml`

All these conflicts are because glitch-soc and upstream have different theming
systems and upstream changed a few things to have dynamic theme selection based
on system settings.

Conflicts were solved to take that into account, and `current_theme` has been
changed in the process to return a tuple of `[flavour, skin]` to be used in
the `theme_style_tags` helper.

app/helpers/application_helper.rb

@@ -161,6 +161,17 @@ module ApplicationHelper
     output.compact_blank.join(' ')
   end
 
+  def theme_style_tags(flavour_and_skin)
+    flavour, theme = flavour_and_skin
+
+    if theme == 'system'
+      concat stylesheet_pack_tag("skins/#{flavour}/mastodon-light", media: 'not all and (prefers-color-scheme: dark)', crossorigin: 'anonymous')
+      concat stylesheet_pack_tag("skins/#{flavour}/default", media: '(prefers-color-scheme: dark)', crossorigin: 'anonymous')
+    else
+      stylesheet_pack_tag "skins/#{flavour}/#{theme}", media: 'all', crossorigin: 'anonymous'
+    end
+  end
+
   def cdn_host
     Rails.configuration.action_controller.asset_host
   end