fix(hatch): show fill on creation, not only after a boundary edit

`add_hatch` let `add_entity` build the render model from the new DXF
entity (via `hatch_model_from_dxf`, AABB-centred `world_origin`) and
insert it — then overwrote it with the command-built model, whose
`world_origin` is [0, 0]. After the world_offset removal the fill is
drawn relative-to-eye from `world_origin`, so a [0, 0] origin with a
full-WCS boundary cancels to garbage in f32 and the fill renders
off-screen — invisible until a later edit rebuilt it from the DXF.

Drop the overwrite so creation keeps the correct seed; it now matches
what an edit or reload produces. Fixes the regression for hatches drawn
away from the origin.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

src/scene/mod.rs

@@ -5441,11 +5441,13 @@ impl Scene {
             1.0
         };
 
-        let handle = self.add_entity(EntityType::Hatch(dxf));
-        if !handle.is_null() {
-            self.hatches.insert(handle, model);
-        }
-        handle
+        // `add_entity` already builds the render model from the DXF entity via
+        // `hatch_model_from_dxf` and inserts it with a correct `world_origin`
+        // (AABB-centred) for the relative-to-eye fill. The command-built `model`
+        // carries `world_origin: [0, 0]`, which after the world_offset removal
+        // leaves the fill mis-placed and effectively invisible until a later
+        // edit rebuilds it from the DXF — so keep the seed, don't overwrite it.
+        self.add_entity(EntityType::Hatch(dxf))
     }
 
     pub fn clear(&mut self) {