switch install state to db

app/controllers/application_controller.rb

@@ -57,6 +57,6 @@ class ApplicationController < ActionController::Base
   end
 
   def setup_completed?
-    File.exist?(Rails.root.join(".installed"))
+    SetupState.installed?
   end
 end

app/controllers/setup_controller.rb

@@ -11,7 +11,7 @@ class SetupController < ApplicationController
     @user.invitation_accepted_at = Time.current
 
     if @user.save
-      create_installed_marker
+      SetupState.mark_installed!
       session[:user_id] = @user.id
       redirect_to admin_root_path, notice: "Setup complete! Welcome to Sanasto Wiki."
     else
@@ -28,15 +28,7 @@ class SetupController < ApplicationController
   end
 
   def setup_completed?
-    File.exist?(installed_marker_path)
-  end
-
-  def installed_marker_path
-    Rails.root.join(".installed")
-  end
-
-  def create_installed_marker
-    FileUtils.touch(installed_marker_path)
+    SetupState.installed?
   end
 
   def user_params

app/models/setup_state.rb

@@ -0,0 +1,16 @@
+class SetupState < ApplicationRecord
+  def self.installed?
+    first&.installed? || false
+  end
+
+  def self.mark_installed!
+    record = first_or_initialize
+    record.installed = true
+    record.installed_at ||= Time.current
+    record.save!
+  end
+
+  def self.reset!
+    delete_all
+  end
+end