refactor(settings/audit): conditional retention disclosure + flat layout

Drops the wrapping details-card so the audit toggle and retention input
read like the email page. The audit switch now uses role="switch" and a
new app-settings-audit component (built on the existing
createConditionalToggleInit primitive) hides the retention block when
audit is disabled — the input is meaningless without audit on, and the
control state syncs automatically on toggle. The redundant info
blockquote and the toggle's paraphrased DB description are gone.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

tests/Architecture/FrontendRuntimeContractSupport.php

@@ -27,6 +27,7 @@ trait FrontendRuntimeContractSupport
             'web/js/components/app-custom-field-options-toggle.js',
             'web/js/components/app-tenant-sso-toggle.js',
             'web/js/components/app-settings-telemetry.js',
+            'web/js/components/app-settings-audit.js',
             'web/js/components/app-standard-detail-page.js',
             'web/js/components/app-auto-submit.js',
             'modules/bookmarks/web/js/components/app-bookmark-save.js',