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/scene/view/render.rs

@@ -60,7 +60,7 @@ pub struct ViewportData {
     /// by the wire / face3d pipelines as a clip-z bias. WireModels carry no
     /// depth field (84 construction sites); the bias is looked up by handle
     /// at GPU-upload time from this map instead.
-    pub(in crate::scene) draw_depths: Arc<rustc_hash::FxHashMap<u64, f32>>,
+    pub(in crate::scene) draw_depths: Arc<rustc_hash::FxHashMap<u64, [f32; 2]>>,
     pub(in crate::scene) hatches: Arc<Vec<HatchModel>>,
     /// Wipeout fills — rendered in a separate pass AFTER wires.
     pub(in crate::scene) wipeout_hatches: Arc<Vec<HatchModel>>,