provide app url variable for email templates

app/models/reminder_mailing.rb

@@ -7,7 +7,8 @@ class ReminderMailing < ApplicationRecord
     :Einsatz,
     :EinsatzStart,
     :FeedbackLink,
-    :EmailAbsender
+    :EmailAbsender,
+    :OnlinePlattformUrl
   ].freeze
 
   belongs_to :creator, -> { with_deleted }, class_name: 'User', inverse_of: 'reminder_mailings'

app/models/reminder_mailing_volunteer.rb

@@ -121,4 +121,8 @@ class ReminderMailingVolunteer < ApplicationRecord
   def feedback_link
     "[Halbjahres-Rapport erstellen](#{feedback_url})"
   end
+
+  def online_plattform_url
+    "[Online-Plattform Url](#{Rails.application.routes.url_helpers.root_path})"
+  end
 end

app/models/semester_process_mail.rb

@@ -19,7 +19,8 @@ class SemesterProcessMail < ApplicationRecord
     :Einsatz,
     :FeedbackLink,
     :EmailAbsender,
-    :Semester
+    :Semester,
+    :OnlinePlattformUrl
   ].freeze
 
   def self.template_varnames
@@ -87,6 +88,10 @@ class SemesterProcessMail < ApplicationRecord
     )
   end
 
+  def online_plattform_url
+    "[Online-Plattform Url](#{Rails.application.routes.url_helpers.root_path})"
+  end
+
   private
 
   def send_email