Admin protetto, dashboard KPI e aggiornamenti sito marketing.

Login admin con cambio password, metriche server (CPU/RAM/disco/banda), grafici e statistiche streaming; sezione piani ridimensionata.

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

backend/app/controllers/admin/auth_controller.rb

@@ -0,0 +1,25 @@
+module Admin
+  class AuthController < Admin::BaseController
+    skip_before_action :require_admin_login, only: %i[new create]
+
+    def new
+      redirect_to admin_root_path if admin_logged_in?
+    end
+
+    def create
+      account = AdminAccount.find_by(username: params[:username]&.strip)
+      if account&.authenticate(params[:password])
+        session[:admin_account_id] = account.id
+        redirect_to session.delete(:admin_return_to) || admin_root_path, notice: "Accesso effettuato"
+      else
+        flash.now[:alert] = "Username o password non validi"
+        render :new, status: :unauthorized
+      end
+    end
+
+    def destroy
+      reset_session
+      redirect_to admin_login_path, notice: "Disconnesso"
+    end
+  end
+end