Merge commit '379115e601361c2b5da775fbf28b7dff9dc02e71' into glitch-soc/merge-upstream

Conflicts:
- `config/navigation.rb`:
  Conflict due to glitch-soc having extra navigation items for its theming
  system.
  Ported upstream changes.

app/helpers/self_destruct_helper.rb

@@ -0,0 +1,14 @@
+# frozen_string_literal: true
+
+module SelfDestructHelper
+  def self.self_destruct?
+    value = ENV.fetch('SELF_DESTRUCT', nil)
+    value.present? && Rails.application.message_verifier('self-destruct').verify(value) == ENV['LOCAL_DOMAIN']
+  rescue ActiveSupport::MessageVerifier::InvalidSignature
+    false
+  end
+
+  def self_destruct?
+    SelfDestructHelper.self_destruct?
+  end
+end