docs: reorganize documentation — developer-friendly structure

New structure:
- docs/index.md — main navigation
- docs/getting-started.md — 5-minute quick start
- docs/guides/module-manual.md — all 11 modules with file listing
- docs/guides/api-usage.md — API reference with code examples
- docs/guides/ — architecture, building, testing, contributing
- docs/reference/ — competitive analysis, gap analysis, versioning
- docs/api/ — Doxygen generated HTML
- docs/archive/ — historical development plans

Old development plans archived. Clean 4-directory layout.

docs/getting-started.md

@@ -0,0 +1,79 @@
+# 快速入门
+
+> 5 分钟跑起 ViewDesignEngine
+
+## 1. 编译
+
+```bash
+# Docker（推荐，开箱即用）
+docker run --rm -v $(pwd):/ws -w /ws vde-builder:latest \
+  bash -c "cmake -B build && cmake --build build -j$(nproc)"
+
+# 本地（需要 CMake 3.16+, GCC 11+/Clang 16+, Eigen3）
+cmake -B build -DCMAKE_BUILD_TYPE=Release
+cmake --build build -j$(nproc)
+```
+
+## 2. 运行测试
+
+```bash
+cd build && ctest --output-on-failure -E Benchmark
+```
+
+## 3. 第一个程序
+
+```cpp
+#include <vde/brep/modeling.h>
+#include <vde/brep/brep_boolean.h>
+#include <vde/foundation/io_step.h>
+#include <iostream>
+
+using namespace vde::brep;
+
+int main() {
+    // 创建两个实体
+    auto box = make_box(2, 2, 2);       // 2×2×2 立方体
+    auto sphere = make_sphere(1.5, 32);  // 半径1.5球体
+
+    // 布尔并集
+    auto result = brep_union(box, sphere);
+
+    // 验证结果
+    auto report = validate(result);
+    std::cout << "Faces: " << result.num_faces()
+              << " Valid: " << report.valid << std::endl;
+
+    // 导出 STEP
+    export_step_file(result, "output.step");
+
+    return 0;
+}
+```
+
+编译运行：
+```bash
+g++ -std=c++17 -I include -L build/src \
+    my_program.cpp -lvde_brep -lvde_curves -lvde_foundation \
+    -lvde_core -o my_program
+./my_program
+```
+
+## 4. 核心头文件速查
+
+| 功能 | 头文件 | 关键 API |
+|------|--------|---------|
+| 创建基本体 | `vde/brep/modeling.h` | `make_box`, `make_cylinder`, `make_sphere` |
+| 布尔运算 | `vde/brep/brep_boolean.h` | `brep_union`, `brep_intersection`, `brep_difference` |
+| 拓扑修复 | `vde/brep/brep_heal.h` | `heal_topology`, `heal_gaps` |
+| 验证 | `vde/brep/brep_validate.h` | `validate` |
+| STEP 读写 | `vde/foundation/io_step.h` | `import_step_file`, `export_step_file` |
+| 网格转换 | `vde/brep/brep.h` | `body.to_mesh()` |
+| SDF 建模 | `vde/sdf/sdf_tree.h` | SDF 隐式曲面 |
+| CAM 加工 | `vde/core/cam_strategies.h` | `roughing_toolpath`, `finishing_toolpath` |
+| 装配体 | `vde/brep/assembly.h` | `Assembly`, `AssemblyNode` |
+
+## 5. 下一步
+
+- [模块说明书](guides/module-manual.md) — 了解所有模块的能力
+- [API 使用手册](guides/api-usage.md) — 详细 API 使用示例
+- [examples/](../examples/) — 完整可运行示例