Commit iniziale di eminuxCRM: CRM Rails con pipeline, campagne email e Docker.

Include autenticazione, progetti isolati, mail marketing HTML con SMTP, test A/B e editor WYSIWYG.

Co-authored-by: Cursor <cursoragent@cursor.com>

app/models/user_project.rb

@@ -0,0 +1,6 @@
+class UserProject < ApplicationRecord
+  belongs_to :user
+  belongs_to :project
+
+  validates :user_id, uniqueness: { scope: :project_id }
+end