validate prefilled champs when editing brouillon

app/assets/stylesheets/forms.scss

@@ -228,6 +228,10 @@
     }
   }
 
+  div.field_with_errors > input { // scss-lint:disable SelectorFormat
+    border: 1px solid $dark-red;
+  }
+
   input[type=text],
   input[type=email],
   input[type=password],

app/controllers/users/dossiers_controller.rb

@@ -148,7 +148,7 @@ module Users
 
     def brouillon
       @dossier = dossier_with_champs
-      # TODO: SEB show validation errors
+      @dossier.valid?(context: :prefilling)
 
       # TODO: remove when the champs are unifed
       if !@dossier.autorisation_donnees

app/models/dossier.rb

@@ -435,6 +435,8 @@ class Dossier < ApplicationRecord
   validates :individual, presence: true, if: -> { revision.procedure.for_individual? }
   validates :groupe_instructeur, presence: true, if: -> { !brouillon? }
 
+  validates_associated :champs_public, on: :prefilling
+
   def types_de_champ_public
     types_de_champ
   end