feat(studio): award-tier visual polish

Brightness-aware elevation tokens (FaiElevation low/medium) applied
to cards, sheets and the sidebar active item; gentle hover-lift on
Store + Doc cards; a longer, eased sidebar expand using the
under-used FaiMotion.slow; and a branded empty state carrying the
F∆I delta mark with warmer spacing. Subtle, Linear/Raycast-style —
both light and dark themes tuned.

Signed-off-by: flemming-it <stefan.a.flemming@googlemail.com>

lib/widgets/fai_module_sheet.dart

@@ -26,6 +26,7 @@ class FaiModuleSheet extends StatefulWidget {
       context: context,
       backgroundColor: Theme.of(context).colorScheme.surfaceContainer,
       isScrollControlled: true,
+      elevation: 8,
       shape: const RoundedRectangleBorder(
         borderRadius: BorderRadius.vertical(top: Radius.circular(FaiRadius.md)),
       ),