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/app/cmd_result.rs

@@ -125,6 +125,16 @@ impl OpenCADStudio {
                 self.tabs[i].snap_result = None;
                 self.restore_pre_cmd_tangent();
             }
+            CmdResult::CommitSolid { entity, solid } => {
+                let label = self.history_label_from_active_cmd(i, "SOLID");
+                self.push_undo_snapshot(i, label);
+                self.add_model_solid(entity, *solid);
+                self.tabs[i].dirty = true;
+                self.tabs[i].scene.clear_preview_wire();
+                self.tabs[i].active_cmd = None;
+                self.tabs[i].snap_result = None;
+                self.restore_pre_cmd_tangent();
+            }
             CmdResult::CommitAndEditText(entity) => {
                 let label = self.history_label_from_active_cmd(i, "ENTITY");
                 self.push_undo_snapshot(i, label);