fix: Use inset outline-offset so focus ring is visible inside overflow:hidden parent

The stacked layout content area has overflow:hidden, which clips outlines
rendered outside the element box. Using a negative outline-offset renders
the focus ring inside the element, making it visible.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

Author: uzirthapa

packages/component/src/Activity/StackedLayout.module.css

@@ -61,6 +61,7 @@
       outline: var(--webchat__border-width--transcript-visual-keyboard-indicator)
         var(--webchat__border-style--transcript-visual-keyboard-indicator)
         var(--webchat__color--transcript-visual-keyboard-indicator);
+      outline-offset: calc(-1 * var(--webchat__border-width--transcript-visual-keyboard-indicator));
     }
   }