Display tessellation plans (1/4): planner with shared edge nodes (#802)

Adds TessPlan and the kernel planner (shared edge nodes, structured and Coons grids, constrained Delaunay for trimmed faces) behind Body::display_plan. Nothing drawn changes yet.

Refs #303

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

Cargo.toml

@@ -37,6 +37,9 @@ truck-shapeops = { version = "0.4", default-features = false }
 truck-meshalgo = { version = "0.4", default-features = false, features = ["tessellation", "analyzers"] }
 truck-stepio = { version = "0.3", default-features = false }
 truck-topology = "0.6"
+# constrained Delaunay + Ruppert refinement for trimmed faces (MIT OR Apache-2.0); already in the
+# tree through truck-meshalgo.
+spade = { version = "2.15", default-features = false, features = ["std"] }
 
 # packages (3MF)
 zip = { version = "3", default-features = false, features = ["deflate"] }