feat(3d): instance block-definition solid meshes per INSERT

3D solid meshes inside block definitions were drawn once at block-local
coordinates without the INSERT transform, so a block authored in mm and
placed into a metre drawing at a 0.001 INSERT scale rendered ~1000x too
large. Split solid meshes into top-level (layout-owned, offset and drawn
flat) and block-definition (kept block-local) sets, and emit a transformed
instance of each block-def mesh per model-space INSERT, accumulating nested
transforms. Layout blocks are identified from the Layout objects'
block_record handles, since BlockRecord::is_layout() also flags ordinary
blocks in some files. (#123)

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

src/app/update.rs

@@ -567,6 +567,7 @@ impl OpenCADStudio {
                 self.tabs[i].scene.hatches = caches.hatches;
                 self.tabs[i].scene.images = caches.images;
                 self.tabs[i].scene.meshes = caches.meshes;
+                self.tabs[i].scene.block_meshes = caches.block_meshes;
                 // Invalidate the wire cache so the new document is tessellated.
                 self.tabs[i].scene.bump_geometry();
                 self.tabs[i].scene.selected = rustc_hash::FxHashSet::default();