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, 7 insertions, 2 deletions

diff --git a/src/mainwindow.cpp b/src/mainwindow.cpp
index 19373e3..e93898c 100644
--- a/src/mainwindow.cpp
+++ b/src/mainwindow.cpp
@@ -962,8 +962,13 @@ void MainWindow::buildUi()
     // the viewport and auto-scroll brought the clicked index fully into view.
     m_threadView->setHorizontalScrollBarPolicy(Qt::ScrollBarAlwaysOff);
 
-    // Scrolling a whole card at a time rather than a fraction of one, so a
-    // card is never left half above the top edge.
+    // Per PIXEL, so a touchpad moves the list continuously. Qt's default is
+    // per ITEM, which jumped several whole cards per wheel notch and quantised
+    // a touchpad's small deltas into card-sized jumps, so the eye lost track
+    // of how far the list had moved. The cost is that a card can rest half
+    // above the top edge. A wheel notch glides one step, which is one card;
+    // see ThreadListView::wheelEvent.
+    m_threadView->setVerticalScrollMode(QAbstractItemView::ScrollPerPixel);
     m_threadView->verticalScrollBar()->setSingleStep(
         CardLayout::heightFor(m_threadView->font()));