Add “Update available” navigation item at top of navbar when new Mastodon versions are available (#39705)

app/javascript/material-icons/400-24px/system_update_alt-fill.svg

@@ -0,0 +1 @@
+<svg xmlns="http://www.w3.org/2000/svg" height="24" viewBox="0 -960 960 960" width="24"><path d="M160-160q-33 0-56.5-23.5T80-240v-480q0-33 23.5-56.5T160-800h200v80H160v480h640v-480H600v-80h200q33 0 56.5 23.5T880-720v480q0 33-23.5 56.5T800-160H160Zm320-184L280-544l56-56 104 104v-304h80v304l104-104 56 56-200 200Z"/></svg>

app/javascript/material-icons/400-24px/system_update_alt.svg

@@ -0,0 +1 @@
+<svg xmlns="http://www.w3.org/2000/svg" height="24" viewBox="0 -960 960 960" width="24"><path d="M160-160q-33 0-56.5-23.5T80-240v-480q0-33 23.5-56.5T160-800h200v80H160v480h640v-480H600v-80h200q33 0 56.5 23.5T880-720v480q0 33-23.5 56.5T800-160H160Zm320-184L280-544l56-56 104 104v-304h80v304l104-104 56 56-200 200Z"/></svg>

app/models/software_update.rb

@@ -47,6 +47,10 @@ class SoftwareUpdate < ApplicationRecord
       all.to_a.filter(&:pending?)
     end
 
+    def pending?
+      pending_to_a.present?
+    end
+
     def urgent_pending?
       pending_to_a.any?(&:urgent?)
     end