Refine tool call summaries and scrolling (#2069)

* feat(app): refine tool call summaries and scrolling

Keep summary groups stable from the first tool call, preserve live activity feedback, and scroll expanded groups to the latest entry. Consolidate web scrollbar styling around the native browser mechanism.

* refactor(app): reuse tool call height constant

* fix(app): preserve tool call summary state

* fix(app): refresh web tool groups on expand

* fix(app): preserve grouped tool errors

packages/app/src/components/diff-scroll.web.tsx

@@ -1,6 +1,5 @@
-import { useCallback, useMemo } from "react";
+import { useCallback } from "react";
 import { ScrollView, type LayoutChangeEvent, type StyleProp, type ViewStyle } from "react-native";
-import { useWebScrollbarStyle } from "@/hooks/use-web-scrollbar-style";
 
 interface DiffScrollProps {
   children: React.ReactNode;
@@ -16,8 +15,6 @@ export function DiffScroll({
   style,
   contentContainerStyle,
 }: DiffScrollProps) {
-  const webScrollbarStyle = useWebScrollbarStyle();
-  const combinedStyle = useMemo(() => [style, webScrollbarStyle], [style, webScrollbarStyle]);
   const handleLayout = useCallback(
     (e: LayoutChangeEvent) => onScrollViewWidthChange(e.nativeEvent.layout.width),
     [onScrollViewWidthChange],
@@ -28,7 +25,7 @@ export function DiffScroll({
       horizontal
       nestedScrollEnabled
       showsHorizontalScrollIndicator
-      style={combinedStyle}
+      style={style}
       contentContainerStyle={contentContainerStyle}
       onLayout={handleLayout}
     >