Polish floating bottom bar: elevation, height, overlap, and FAB shape

- Give the floating bar and search satellite the app's one shadow
  (nooDialogShadow) plus a smaller, tighter height on both platforms.
- Let every tab's scrollable list compute its own bottom clearance
  (bottomBarClearance) instead of a flat 100px, so the floating bar no
  longer overlaps the last row/card.
- Square the Android upload FAB off to a rounded-square radius when the
  bottom bar is attached, keeping it fully round only when floating.
- Let a swipe on a file row trigger its action directly once dragged
  past 1.8x the reveal width, instead of requiring a second tap.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

lib/views/shares_view.dart

@@ -120,7 +120,7 @@ class _SharesViewState extends State<SharesView> {
         _buildDesktopTable(context, shares)
       else
         _buildMobileList(context, shares),
-      ...tabBottomInsetSlivers,
+      ...tabBottomInsetSlivers(context),
     ];
 
     return ColoredBox(