feat: update dropdown shadow to match Pine's visual prominence (#2142)

- Change sage-dropdown__panel from sage-shadow(md) to sage-shadow(100)
- Matches Pine's --pine-box-shadow-100 for consistent visual prominence
- Addresses DSS-1493

The sage-shadow(100) token has identical shadow values to Pine's
--pine-box-shadow-100: 0 1px 3px 0 rgba(0,0,0,.1), 0 1px 2px 0 rgba(0,0,0,.06)
ensuring perfect visual matching while maintaining design system consistency.

Co-authored-by: Devin AI <158243242+devin-ai-integration[bot]@users.noreply.github.com>

Author: camsimony

packages/sage-assets/lib/stylesheets/components/_dropdown.scss

@@ -346,7 +346,7 @@ $-dropdown-trigger-dropdown-offset: rem(16px) + sage-spacing(xs);
   width: auto;
   border-radius: sage-border(radius-medium);
   background-color: sage-color(white);
-  box-shadow: sage-shadow(md);
+  box-shadow: sage-shadow(100);
   transition: map-get($sage-transitions, default);
   transition-property: transform, z-index;