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/securities_controller.rb

@@ -6,5 +6,6 @@ class Settings::SecuritiesController < ApplicationController
       [ "Home", root_path ],
       [ "Security", nil ]
     ]
+    @oidc_identities = Current.user.oidc_identities.order(:provider)
   end
 end