Face-tagged 3MF exchange: format spec, reader, geometry.import.mesh

docs/formats/tagged-mesh.md defines the exchange: 3MF Core with an optional
ft:face attribute per triangle (and ft:faces per object) in a ModelCraft
namespace. modelcraft_geometry::tagged_mesh::read_3mf reads it from bytes
(wasm), capping every size and count and range-checking every index and
coordinate. geometry.import.mesh adds the surfaces to the session, which keeps
them beside the open design and restores them when a command fails.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01NmAttHhUZTokgPeEJia8sm

crates/engine/Cargo.toml

@@ -15,3 +15,6 @@ serde = { workspace = true }
 serde_json = { workspace = true }
 thiserror = { workspace = true }
 log = { workspace = true }
+
+[dev-dependencies]
+zip = { workspace = true }