feat(v4.3): wall thickness analysis — centroid-offset sampling

- analyze_wall_thickness(): samples surface points, computes min distance
  to vertices/centroids on other faces (no mesh tessellation needed)
- WallThicknessResult: min/max/avg, thin_threshold, thick_threshold
- 3 new tests, 29/29 passing

include/vde/brep/measure.h

@@ -60,4 +60,24 @@ struct BomEntry {
 /// 生成扁平合并的物料清单（按名称排序）
 [[nodiscard]] std::vector<BomEntry> generate_bom(const AssemblyNode& node);
 
+// ── Wall thickness analysis ──
+
+/// 壁厚分析结果
+struct WallThicknessResult {
+    double min_thickness = 0.0;      ///< 最小壁厚
+    double max_thickness = 0.0;      ///< 最大壁厚
+    double avg_thickness = 0.0;      ///< 平均壁厚
+    int thin_regions = 0;            ///< 薄壁区域数（< thin_threshold）
+    int thick_regions = 0;           ///< 厚壁区域数（> thick_threshold）
+    double thin_threshold = 1.0;     ///< 薄壁判定阈值
+    double thick_threshold = 10.0;   ///< 厚壁判定阈值
+};
+
+/// 壁厚分析：沿各面法向采样，射线检测对面距离
+/// @param body B-Rep 实体
+/// @param samples_per_face 每个面的采样点数（默认 5×5=25）
+/// @return 壁厚统计结果
+[[nodiscard]] WallThicknessResult analyze_wall_thickness(const BrepModel& body,
+    int samples_per_face = 5);
+
 } // namespace vde::brep