fix(paper): keep model 3D solids off the paper-space sheet

The paper layout sheet pass reused the full model mesh set, so every
top-level 3D solid piled onto the paper origin — the sheet camera works
in paper coordinates, not model space. Guard `meshes` on
`inst.paper_sheet` the same way wires/hatches/images already are: the
sheet shows only paper-native content; the model's solids render inside
the floating content viewports (model camera + per-viewport scissor).

Also name 3DSOLID/REGION/BODY/SURFACE/MESH/SOLID/MULTILEADER in dxf_name
(they fell through to "ENTITY"), and add a SELHANDLES diagnostic that
reports the active space plus a per-type / per-block selection breakdown.

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

src/entities/names.rs

@@ -92,8 +92,15 @@ pub fn dxf_name(e: &EntityType) -> &'static str {
         EntityType::AttributeDefinition(_) => "ATTDEF",
         EntityType::AttributeEntity(_) => "ATTRIB",
         EntityType::Leader(_) => "LEADER",
+        EntityType::MultiLeader(_) => "MULTILEADER",
         EntityType::Tolerance(_) => "TOLERANCE",
         EntityType::Shape(_) => "SHAPE",
+        EntityType::Solid(_) => "SOLID",
+        EntityType::Solid3D(_) => "3DSOLID",
+        EntityType::Region(_) => "REGION",
+        EntityType::Body(_) => "BODY",
+        EntityType::Surface(_) => "SURFACE",
+        EntityType::Mesh(_) => "MESH",
         _ => "ENTITY",
     }
 }