refactor: remove SSO settings page; consolidate SSO identity management under Security settings

- Removed the `Settings::SsoIdentitiesController` and views for a simplified user experience.
- Moved SSO identity management to the Security settings page (`Settings::SecuritiesController`).
- Updated locale keys and layout for the new structure.
- Fixed unlink protection warnings and adjusted redirection path.
- Cleaned up routes, helper methods, and redundant code.

app/controllers/settings/sso_identities_controller.rb

@@ -3,20 +3,12 @@
 class Settings::SsoIdentitiesController < ApplicationController
   layout "settings"
 
-  def show
-    @oidc_identities = Current.user.oidc_identities.order(:provider)
-    @breadcrumbs = [
-      [ t("settings.nav.home"), root_path ],
-      [ t(".page_title"), nil ]
-    ]
-  end
-
   def destroy
     @identity = Current.user.oidc_identities.find(params[:id])
 
     # Prevent unlinking last identity if user has no password
     if Current.user.oidc_identities.count == 1 && Current.user.password_digest.blank?
-      redirect_to settings_sso_identities_path, alert: t(".cannot_unlink_last")
+      redirect_to settings_security_path, alert: t(".cannot_unlink_last")
       return
     end
 
@@ -30,6 +22,6 @@ class Settings::SsoIdentitiesController < ApplicationController
       request: request
     )
 
-    redirect_to settings_sso_identities_path, notice: t(".success", provider: provider_name)
+    redirect_to settings_security_path, notice: t(".success", provider: provider_name)
   end
 end