spreadsheet: negate wheel deltas to the ScrollRegion sign convention

The MouseWheel arm fed raw event deltas into the inertial velocity while
every other scrollable widget (ScrollRegion, TextBox) negates them, so the
spreadsheet re-inverted the natural-scroll inversion libinput already
applied and scrolled backwards relative to the rest of the DE.

Co-Authored-By: Claude Fable 5 <[email protected]>

 src/widget/container/spreadsheet.rs | 16 +++++++++-------
 1 file changed, 9 insertions(+), 7 deletions(-)

diff --git a/src/widget/container/spreadsheet.rs b/src/widget/container/spreadsheet.rs
index 361d770..fe0daa4 100644
--- a/src/widget/container/spreadsheet.rs
+++ b/src/widget/container/spreadsheet.rs
@@ -512,9 +512,11 @@ impl Input for Spreadsheet {
             }
             // Hit-gated by the adapter (which also rejects hidden widgets).
             Event::MouseWheel { delta, .. } => {
+                // Delta signs follow the ScrollRegion/TextBox convention (negate the
+                // event delta); natural scroll is already applied upstream by libinput.
                 let (dx, dy) = match delta {
-                    MouseScrollDelta::LineDelta(x, y) => (*x * ROW_H, *y * ROW_H),
-                    MouseScrollDelta::PixelDelta(pos) => (pos.x as f32, pos.y as f32),
+                    MouseScrollDelta::LineDelta(x, y) => (-*x * ROW_H, -*y * ROW_H),
+                    MouseScrollDelta::PixelDelta(pos) => (-pos.x as f32, -pos.y as f32),
                 };
                 let mut used = false;
                 if dy.abs() > 0.0 && self.geom(ectx.rect).is_some() {
@@ -754,7 +756,7 @@ mod tests {
         ctx.register_widget(id, ptr);
 
         let wheel = Event::MouseWheel {
-            delta: MouseScrollDelta::LineDelta(2.0, 0.0),
+            delta: MouseScrollDelta::LineDelta(-2.0, 0.0),
             x: 50.0,
             y: 60.0,
             local_x: 50.0,
@@ -770,7 +772,7 @@ mod tests {
         let rect = Rect { x: 0.0, y: 0.0, width: 200.0, height: 124.0 };
         let max = (*s).hgeom(rect).unwrap().max_scroll;
         assert!((*s).scroll_x >= 0.0 && (*s).scroll_x <= max, "h-scroll stays clamped");
-        assert!((*s).scroll_x > 0.0, "positive dx scrolled the columns");
+        assert!((*s).scroll_x > 0.0, "negative dx scrolled the columns (ScrollRegion sign convention)");
 
         // A pane whose columns fit ignores horizontal wheels.
         let mut fits = wide(2);
@@ -786,10 +788,10 @@ mod tests {
         let (id, ptr) = (s.id(), s.as_ptr_mut());
         ctx.register_widget(id, ptr);
 
-        // A wheel over the body feeds velocity (scroll down = negative line delta in practice,
-        // but sign just follows the delta)…
+        // A wheel over the body feeds velocity (negated delta, the ScrollRegion
+        // convention: a negative line delta scrolls the view down)…
         let wheel = Event::MouseWheel {
-            delta: MouseScrollDelta::LineDelta(0.0, 2.0),
+            delta: MouseScrollDelta::LineDelta(0.0, -2.0),
             x: 50.0,
             y: 60.0,
             local_x: 50.0,