Introduce an "owner" role, and prevent it from being administered

to prevent the owner from being demoted or kicked out.

ref: https://app.fizzy.do/5986089/cards/3213

db/migrate/20251129175717_promote_first_admin_to_owner.rb

@@ -0,0 +1,14 @@
+class PromoteFirstAdminToOwner < ActiveRecord::Migration[8.2]
+  def up
+    Account.find_each do |account|
+      next if account.users.exists?(role: :owner)
+
+      first_admin = account.users.where(role: :admin).order(:created_at).first
+      first_admin&.update!(role: :owner)
+    end
+  end
+
+  def down
+    User.where(role: :owner).update_all(role: :admin)
+  end
+end