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/theme/design_tokens.dart

@@ -356,8 +356,9 @@ class NooMotion {
 }
 
 /// The one shadow the design system allows, from `tokens/spacing.css`'s
-/// `--shadow-dialog` - desktop dialogs only. Nothing else in the app should
-/// use a `BoxShadow`.
+/// `--shadow-dialog` - desktop dialogs, and [NooBottomBarStyle.floating]'s
+/// bar/search satellite (the only other thing in the app that's genuinely
+/// floating above other content). Nothing else should use a `BoxShadow`.
 const nooDialogShadow = BoxShadow(
   color: Color(0x241E002F), // rgba(30,0,47,.14)
   blurRadius: 48,