feat: scroll the thread list smoothlyHEADmaster

The list scrolled per ITEM, Qt's default, so a wheel notch jumped
several whole cards at once and a touchpad's small deltas were
quantised into card-sized jumps. The eye lost track of how far the
list had moved.

The view now scrolls per pixel, so a touchpad moves it continuously,
and ThreadListView::wheelEvent turns each wheel notch into a 160ms
eased glide of exactly one card. Notches arriving mid-glide add to its
target rather than restarting from where it has got to. Pixel deltas
and modified wheels pass through to Qt unchanged. The cost of per-pixel
scrolling is that a card can rest half above the top edge.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

1 files changed, 13 insertions, 0 deletions

diff --git a/src/threadlistview.h b/src/threadlistview.h
index a509389..79db424 100644
--- a/src/threadlistview.h
+++ b/src/threadlistview.h
@@ -20,6 +20,8 @@
 
 #include <QTreeView>
 
+class QPropertyAnimation;
+
 /// The thread list.
 ///
 /// It exists for ONE reason now: the expander is drawn by CardDelegate, and a
@@ -47,4 +49,15 @@ protected:
     /// indicator underneath, also removed the style's hit area, so an expander
     /// once painted correctly and did nothing at all.
     void mousePressEvent(QMouseEvent *event) override;
+
+    /// A mouse wheel notch GLIDES one scrollbar step instead of jumping, so
+    /// the eye can follow how far the list moved. Notches arriving mid-glide
+    /// add to its target rather than restarting from where it has got to. A
+    /// touchpad's pixel deltas are already continuous and pass straight
+    /// through, as does any wheel with a modifier held.
+    void wheelEvent(QWheelEvent *event) override;
+
+private:
+    /// Created on the first notch, owned by the view.
+    QPropertyAnimation *m_glide = nullptr;
 };