fix(xref): blocks respect their internal draw order

Xref merge now inserts entities in the source block's chain order and
carries SortEntitiesTable objects across (remapped to merged handles).
draw_depth_map values become [depth, half] so exploded block/xref fills
and wide-polyline band wires both compose child depth as
insert_depth + in-block rank x half, recursing into nested inserts with
the same divisor - bands and fills from one block interleave by the
block's internal order instead of stacking at the insert's single depth.
Band batches split per rank via WireModel.depth_override; thin wires
stay merged. The wire arena falls back to a full rebuild when a slab
carries mixed depths so refreshes don't flatten band overrides.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

src/modules/view/zoom_window.rs

@@ -67,6 +67,7 @@ impl CadCommand for ZoomWindowCommand {
         Some(WireModel {
             taper_widths: Vec::new(),
             world_width: 0.0,
+            depth_override: None,
             fill_is_3d: false,
             pick_tris: Vec::new(),
             pick_tris_low: Vec::new(),