feat: implement flash messages system with auto-dismiss notifications

- Add flash message helper and styles for consistent notifications
- Replace Devise error messages with flash-based notifications
- Add dashboard page with event statistics
- Configure SMTP settings for development and production
- Update authentication controllers to use flash messages
- Add JavaScript controller for auto-dismiss functionality

app/controllers/authentications/sessions_controller.rb

@@ -9,9 +9,10 @@ class Authentications::SessionsController < Devise::SessionsController
   # end
 
   # POST /resource/sign_in
-  # def create
-  #   super
-  # end
+  def create
+    super
+    flash[:notice] = "Connexion réussie !" if resource.persisted?
+  end
 
   # DELETE /resource/sign_out
   # def destroy