feat: add GUI mvp

src/app/gui/smooth_scroll.py

@@ -0,0 +1,60 @@
+from __future__ import annotations
+
+from PySide6 import QtCore, QtWidgets
+
+
+class _SmoothWheelFilter(QtCore.QObject):
+    def __init__(self, area: QtWidgets.QAbstractScrollArea, *, duration_ms: int = 140) -> None:
+        super().__init__(area)
+        self._area = area
+        self._duration_ms = max(60, int(duration_ms))
+        self._anim = QtCore.QPropertyAnimation(area.verticalScrollBar(), b"value", self)
+        self._anim.setEasingCurve(QtCore.QEasingCurve.Type.OutCubic)
+
+    def eventFilter(self, obj: QtCore.QObject, event: QtCore.QEvent) -> bool:  # noqa: N802
+        if event.type() != QtCore.QEvent.Type.Wheel:
+            return super().eventFilter(obj, event)
+
+        wheel = event  # type: ignore[assignment]
+        try:
+            angle_y = wheel.angleDelta().y()
+            pixel_y = wheel.pixelDelta().y()
+        except Exception:
+            return super().eventFilter(obj, event)
+
+        dy = pixel_y if pixel_y else angle_y
+        if dy == 0:
+            return True
+
+        sb = self._area.verticalScrollBar()
+        start = sb.value()
+
+        # Map a wheel "step" to a reasonable pixel delta; keep it snappy but not jarring.
+        base_step = 80
+        if pixel_y:
+            delta = -dy
+        else:
+            delta = int(round(-dy / 120.0 * base_step))
+
+        target = max(sb.minimum(), min(sb.maximum(), start + delta))
+        if target == start:
+            return True
+
+        self._anim.stop()
+        self._anim.setDuration(self._duration_ms)
+        self._anim.setStartValue(start)
+        self._anim.setEndValue(target)
+        self._anim.start()
+        return True
+
+
+def enable_smooth_scrolling(widget: QtWidgets.QAbstractScrollArea, *, duration_ms: int = 140) -> None:
+    """
+    Enables animated wheel scrolling for QAbstractScrollArea-derived widgets
+    (QListWidget, QTableWidget, QPlainTextEdit, etc.).
+    """
+    filt = _SmoothWheelFilter(widget, duration_ms=duration_ms)
+    widget.viewport().installEventFilter(filt)
+    # Keep a reference to avoid the filter being GC'd.
+    widget.setProperty("_smooth_wheel_filter", filt)
+