feat(model): 3D solid modelling tab — primitives + boolean ops

Rename the Home tab to "Draw" and add a Model tab beside it with two
groups:

- Model: BOX / CYLINDER / CONE / SPHERE / WEDGE / TORUS, placed with a
  footprint + height. Each is built as a real ACIS Solid3D (acadrust
  primitive builders) plus a truck B-rep, tessellated into the shaded
  mesh pipeline, with edge wires for picking + wireframe.
- Design: UNION / SUBTRACT / INTERSECT via truck-shapeops.

A session-only Scene.model_solids cache holds each solid's truck B-rep
so the boolean tools can combine and chain them. Supersedes the old
command-line BOX/SPHERE/CYLINDER (insert::solid3d_cmds keeps EXTRUDE/
REVOLVE/SWEEP/LOFT).

Known limitations: booleans need solids created this session; curved
ACIS primitives render in-session but not after reload (the SAT
tessellator handles only planar caps); geometry assumes world_offset 0.

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

src/modules/model/boolean_cmd.rs

@@ -0,0 +1,27 @@
+// Boolean operations on 3D solids (Design group). The actual CSG runs in
+// `App::solid_boolean` (src/app/model_ops.rs) using truck-shapeops on the
+// session-cached truck B-reps; this module just names the operations.
+
+/// Which boolean a Design-group tool performs on the two selected solids.
+#[derive(Clone, Copy, PartialEq, Eq, Debug)]
+pub enum BoolOp {
+    Union,
+    Subtract,
+    Intersect,
+}
+
+impl BoolOp {
+    pub fn from_id(id: &str) -> Option<BoolOp> {
+        Some(match id {
+            "UNION" => BoolOp::Union,
+            "SUBTRACT" => BoolOp::Subtract,
+            "INTERSECT" => BoolOp::Intersect,
+            _ => return None,
+        })
+    }
+}
+
+// ── Autocomplete registry ─────────────────────────────────
+inventory::submit!(crate::command::CommandRegistration {
+    names: &["UNION", "SUBTRACT", "INTERSECT"]
+});