feat(v4.3): BOM (bill of materials) — flat merged, name-sorted

- BomEntry struct: name, quantity, volume, total_volume
- generate_bom(): recursive assembly traversal, same-name merging
- 5 new tests, 26/26 passing

tests/brep/test_measure.cpp

@@ -176,3 +176,51 @@ TEST(AssemblyMassTest, EmptyAssembly) {
     auto mp = assembly_mass_properties(assy.root);
     EXPECT_NEAR(mp.volume, 0.0, 1e-10);
 }
+
+// ═══════════════════════════════════════════════════════════
+//  BOM (Bill of Materials)
+// ═══════════════════════════════════════════════════════════
+
+TEST(BomTest, SinglePart) {
+    Assembly assy("test");
+    assy.root.add_part("bracket", make_box(2, 2, 2));
+    auto bom = generate_bom(assy.root);
+    ASSERT_EQ(bom.size(), 1u);
+    EXPECT_EQ(bom[0].name, "bracket");
+    EXPECT_EQ(bom[0].quantity, 1);
+}
+
+TEST(BomTest, MultipleSameParts) {
+    Assembly assy("test");
+    assy.root.add_part("bolt", make_box(1, 1, 1));
+    assy.root.add_part("bolt", make_box(1, 1, 1));
+    assy.root.add_part("bolt", make_box(1, 1, 1));
+    auto bom = generate_bom(assy.root);
+    ASSERT_EQ(bom.size(), 1u);
+    EXPECT_EQ(bom[0].quantity, 3);
+}
+
+TEST(BomTest, DifferentParts) {
+    Assembly assy("test");
+    assy.root.add_part("base", make_box(4, 4, 1));
+    assy.root.add_part("pillar", make_cylinder(1, 8));
+    assy.root.add_part("top", make_box(4, 4, 1));
+    auto bom = generate_bom(assy.root);
+    ASSERT_EQ(bom.size(), 3u);
+}
+
+TEST(BomTest, NestedBom) {
+    Assembly assy("test");
+    auto* sub = assy.root.add_subassembly("sub_assy");
+    sub->add_part("pin", make_cylinder(0.5, 2));
+    sub->add_part("pin", make_cylinder(0.5, 2));
+    assy.root.add_part("frame", make_box(5, 5, 1));
+    auto bom = generate_bom(assy.root);
+    EXPECT_GE(bom.size(), 2u);
+}
+
+TEST(BomTest, EmptyAssembly) {
+    Assembly assy("test");
+    auto bom = generate_bom(assy.root);
+    EXPECT_TRUE(bom.empty());
+}