fix(diff): keep header controls and horizontal scroll within the panel when line wrap is off

In the changes/diff view, an unwrapped diff's intrinsic width leaked up the
flex chain: the flex-1 column holding the scroll area lacked min-width:0, so its
min-content (the widest line) stretched it — and every nested w-full element,
including the .pierre-diff-wrapper (overflow-x-auto) and the file header — grew
to the content width. That pushed the header's action controls past the narrow
viewport and left overflow-x-auto with nothing to scroll.

Add min-w-0 to the diff layout's flex items so the chain stays at viewport
width: long lines now scroll horizontally inside the diff, and the file header
controls stay visible.

packages/ui/src/components/views/DiffView.tsx

@@ -1484,7 +1484,7 @@ export const DiffView: React.FC<DiffViewProps> = ({
         };
 
         return (
-            <div className={cn('flex flex-1 min-h-0 h-full', flushContent ? 'gap-0' : 'gap-3 px-3 pb-3 pt-2')}>
+            <div className={cn('flex min-w-0 flex-1 min-h-0 h-full', flushContent ? 'gap-0' : 'gap-3 px-3 pb-3 pt-2')}>
                 {showFileSidebar && (
                     <section className="hidden lg:flex w-72 flex-col rounded-xl border border-border/60 bg-background/70 overflow-hidden">
                         <div className="flex items-center justify-between px-3 py-1.5 border-b border-border/40">
@@ -1498,7 +1498,7 @@ export const DiffView: React.FC<DiffViewProps> = ({
                         />
                     </section>
                 )}
-                <div className="relative flex-1 min-h-0 h-full">
+                <div className="relative flex-1 min-w-0 min-h-0 h-full">
                     <ScrollableOverlay
                         ref={diffScrollRef}
                         outerClassName="min-h-0 h-full"