fix feed scroll reset on device rotation

Remove the dead contentOffset prop from List and add
maintainVisibleContentPosition to anchor the visible item across
relayouts.

The negative contentOffset was originally paired with a matching
contentInset (web PR #230) so the first render sat flush under the
floating header. PR #2216 swapped the inset for a paddingTop style but
left the offset behind, where it's been dead on initial render since.
On rotation its value changes (it's partly derived from the top safe
-area inset), and RN re-applies it as an absolute scroll, snapping the
list. maintainVisibleContentPosition then keeps the visible post pinned
as items reflow to the new width.

APP-2315

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

src/view/com/util/List.tsx

@@ -147,17 +147,19 @@ let List = forwardRef<ListMethods, ListProps>(
       )
     }
 
-    let contentOffset
     if (headerOffset != null) {
       style = addStyle(style, {
         paddingTop: headerOffset,
       })
-      contentOffset = {x: 0, y: headerOffset * -1}
     }
 
     return (
       <FlatList_INTERNAL
         showsVerticalScrollIndicator // overridable
+        // Anchor the currently-visible item across content relayouts so that
+        // changing the viewport size (e.g. device rotation) doesn't lose the
+        // scroll position as items reflow to the new width.
+        maintainVisibleContentPosition={{minIndexForVisible: 0}}
         onViewableItemsChanged={onViewableItemsChanged}
         viewabilityConfig={viewabilityConfig}
         {...props}
@@ -170,7 +172,6 @@ let List = forwardRef<ListMethods, ListProps>(
           ...props.scrollIndicatorInsets,
         }}
         indicatorStyle={t.scheme === 'dark' ? 'white' : 'black'}
-        contentOffset={contentOffset}
         refreshControl={refreshControl}
         onScroll={scrollHandler}
         scrollsToTop={scrollsToTop}