fix(app): restore file tree layout

Restore the established tree rails while retaining file actions. Keep Escape local to generic editable fields so cancelling a file draft cannot interrupt an agent.

packages/app/src/git/diff-pane.tsx

@@ -1161,7 +1161,6 @@ const DiffFileHeader = memo(function DiffFileHeader({
         ref={dragSourceRef}
         style={showDir ? styles.fileHeaderLeft : [styles.fileHeaderLeft, styles.fileHeaderLeftTree]}
       >
-        {showDir ? null : <View style={styles.fileChevronSpacer} />}
         {showDir ? null : (
           <View style={styles.fileIcon}>
             <MaterialFileIcon fileName={fileName} size={WORKSPACE_TREE_ICON_SIZE} />
@@ -3465,11 +3464,6 @@ const styles = StyleSheet.create((theme) => ({
     gap: theme.spacing[1],
     flexShrink: 0,
   },
-  fileChevronSpacer: {
-    width: WORKSPACE_TREE_ICON_SIZE,
-    height: WORKSPACE_TREE_ICON_SIZE,
-    flexShrink: 0,
-  },
   fileIcon: {
     width: WORKSPACE_TREE_ICON_SIZE,
     height: WORKSPACE_TREE_ICON_SIZE,