refactor: rely on platform scroll physics and add scroll behavior tests

README.md

@@ -95,10 +95,15 @@ would mean scrolling back to the top just to change what you are looking at.
 Shifts keeps its whole header fixed for the same reason — the Booked / Open /
 History switch has to stay reachable.
 
-Scrolling uses bouncing physics on every platform (`KrowScrollBehavior`). Under
-a pinned header a rubber-band edge tells you that you have reached the end of
-the content rather than the end of the screen; clamping just stops dead. The
-overscroll glow is turned off, since the bounce already says it.
+Scroll physics is left to the platform. Forcing bouncing everywhere looked
+smoother on a long list and broke every short one: `ScrollView` hands any
+vertical list without a controller an `AlwaysScrollableScrollPhysics`, applied
+over whatever the behaviour returns, so the drag is accepted however little
+content there is. Bouncing then let a list that already fits be dragged away
+from the header, leaving a gap down the screen. Android's clamping accepts the
+same drag and pins it to the boundary; iOS bounces, which is its own
+convention. `KrowScrollBehavior` now only adds mouse and trackpad dragging for
+the web and desktop builds.
 
 Two deliberate exceptions: