feat: P2 B-Rep 内核 + 建模操作

- brep: 完整 B-Rep 数据结构（Vertex/Edge/Loop/Face/Shell/Body）
- brep: 实体工厂（box/cylinder/sphere）
- brep: 建模操作（extrude/revolve/sweep/loft）
- brep: 拓扑查询（face_edges/edge_faces/vertex_edges）
- brep: 网格转换（to_mesh）
- 新增 vde_brep 模块，更新聚合库

include/vde/brep/brep.h

@@ -0,0 +1,67 @@
+#pragma once
+#include "vde/core/point.h"
+#include "vde/core/aabb.h"
+#include "vde/curves/nurbs_curve.h"
+#include "vde/curves/nurbs_surface.h"
+#include "vde/mesh/halfedge_mesh.h"
+#include <vector>
+#include <memory>
+#include <string>
+
+namespace vde::brep {
+
+enum class CurveType { Line, Circle, Bezier, BSpline, Nurbs };
+
+struct TopoVertex { int id; Point3D point; double tolerance = 1e-6; };
+struct TopoEdge {
+    int id, v_start, v_end;
+    std::shared_ptr<curves::NurbsCurve> curve;
+    bool reversed = false;
+};
+struct TopoLoop { int id; std::vector<int> edges; bool is_outer = true; };
+struct TopoFace { int id, surface_id; std::vector<int> loops; bool reversed = false; };
+struct TopoShell { int id; std::vector<int> faces; bool closed = true; };
+struct TopoBody { int id; std::vector<int> shells; std::string name; };
+
+class BrepModel {
+public:
+    BrepModel() = default;
+    int add_vertex(const Point3D& p);
+    int add_edge(int v0, int v1);
+    int add_edge(int v0, int v1, const curves::NurbsCurve& curve);
+    int add_loop(const std::vector<int>& edges, bool outer = true);
+    int add_face(int surface_id, const std::vector<int>& loops);
+    int add_shell(const std::vector<int>& faces, bool closed = true);
+    int add_body(const std::vector<int>& shells, const std::string& name = "");
+    int add_surface(const curves::NurbsSurface& surf);
+
+    [[nodiscard]] size_t num_vertices() const { return vertices_.size(); }
+    [[nodiscard]] size_t num_edges() const { return edges_.size(); }
+    [[nodiscard]] size_t num_faces() const { return faces_.size(); }
+    [[nodiscard]] size_t num_bodies() const { return bodies_.size(); }
+
+    [[nodiscard]] const TopoVertex& vertex(int id) const { return vertices_[id]; }
+    [[nodiscard]] const TopoEdge& edge(int id) const { return edges_[id]; }
+    [[nodiscard]] const TopoFace& face(int id) const { return faces_[id]; }
+    [[nodiscard]] const curves::NurbsSurface& surface(int id) const { return surfaces_[id]; }
+
+    [[nodiscard]] core::AABB3D bounds() const;
+    [[nodiscard]] bool is_valid() const;
+    [[nodiscard]] mesh::HalfedgeMesh to_mesh(double deflection = 0.01) const;
+
+    [[nodiscard]] std::vector<int> face_edges(int face_id) const;
+    [[nodiscard]] std::vector<int> edge_faces(int edge_id) const;
+    [[nodiscard]] std::vector<int> vertex_edges(int vertex_id) const;
+
+private:
+    std::vector<TopoVertex> vertices_;
+    std::vector<TopoEdge> edges_;
+    std::vector<TopoLoop> loops_;
+    std::vector<TopoFace> faces_;
+    std::vector<TopoShell> shells_;
+    std::vector<TopoBody> bodies_;
+    std::vector<curves::NurbsSurface> surfaces_;
+    int next_id_ = 0;
+};
+
+}  // namespace vde::brep

include/vde/brep/modeling.h

@@ -0,0 +1,48 @@
+#pragma once
+#include "vde/brep/brep.h"
+
+namespace vde::brep {
+
+/// Extrude a planar face/wire along a direction
+/// @param profile  Profile curve (must be planar)
+/// @param dir      Extrusion direction (length = distance)
+[[nodiscard]] BrepModel extrude(const curves::NurbsCurve& profile, const Vector3D& dir);
+
+/// Revolve a profile around an axis
+[[nodiscard]] BrepModel revolve(const curves::NurbsCurve& profile,
+                                const Point3D& axis_origin,
+                                const Vector3D& axis_dir,
+                                double angle_rad = 2.0 * M_PI);
+
+/// Sweep a profile along a path curve
+[[nodiscard]] BrepModel sweep(const curves::NurbsCurve& profile,
+                              const curves::NurbsCurve& path);
+
+/// Loft between two or more profile curves
+[[nodiscard]] BrepModel loft(const std::vector<curves::NurbsCurve>& profiles);
+
+/// Create a solid box
+[[nodiscard]] BrepModel make_box(double w, double h, double d);
+
+/// Create a solid cylinder
+[[nodiscard]] BrepModel make_cylinder(double radius, double height, int segments = 32);
+
+/// Create a solid sphere
+[[nodiscard]] BrepModel make_sphere(double radius, int segments_u = 32, int segments_v = 16);
+
+/// Fillet an edge (constant radius)
+/// @param body    Input body
+/// @param edge_id Edge to fillet
+/// @param radius  Fillet radius
+[[nodiscard]] BrepModel fillet(const BrepModel& body, int edge_id, double radius);
+
+/// Chamfer an edge
+[[nodiscard]] BrepModel chamfer(const BrepModel& body, int edge_id, double distance);
+
+/// Shell a solid body (hollow it out)
+/// @param body       Input solid body
+/// @param face_id    Face to remove (opening), -1 for closed shell
+/// @param thickness  Wall thickness (positive = outward offset)
+[[nodiscard]] BrepModel shell(const BrepModel& body, int face_id, double thickness);
+
+}  // namespace vde::brep