refactor(entities): collocate ui_name + dxf_name into entities/names.rs

Two near-identical match-on-EntityType tables lived far apart:
scene/properties.rs::entity_type_name returned mixed-case UI labels;
app/commands.rs::entity_type_name returned uppercase DXF record names.
Both enumerated ~30 variants; adding a new entity meant remembering to
touch two files in two crates' worth of source layout.

Move both into a single entities/names.rs as `ui_name()` and
`dxf_name()`. Adjacent so a new variant gets both labels added at once;
function names make the intended audience explicit at the callsite.

scene/properties.rs and app/commands.rs each lose their local match
plus one re-export, gaining a `crate::entities::names::*` call.

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

src/entities/mod.rs

@@ -13,6 +13,7 @@ pub mod mesh;
 pub mod mline;
 pub mod mtext;
 pub mod multileader;
+pub mod names;
 pub mod ole2frame;
 pub mod point;
 pub mod polyline;