feat: Initial release v0.1.0

STP/STEP 3D viewer (WPF, .NET 8) - CADability + HelixToolkit.Wpf:

- Multi-file import (STEP/STL/DXF) with STEP assembly tree
  (per-node visibility/color cascade, zoom-to)
- Measurements: point / distance / edge / face / circle / angle /
  face-to-face distance (B-rep exact where available)
- Assembly verification: two-point align (translate), 3-point align
  (rotate+translate via RigidAlign), axis rotate 90, interference
  check (tri-tri intersection + min gap)
- Section view (CPU mesh clipping, originals preserved)
- mm/inch toggle, CSV export (UTF-8 BOM), 2x PNG screenshot
- Performance: per-file merged edge lines, per-leaf merged mesh in
  browse mode, no BackMaterial on closed solids, edge suspend during
  camera interaction, parallel leaf triangulation with retry
- SmokeTest CLI: import pipeline, --tree, --clip-test,
  --interference-test, --align-test (all passing)

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

secret/README.md

@@ -0,0 +1,24 @@
+# secret/ — 本機敏感資料集中地
+
+本資料夾除 `README.md` 與 `*.example` 外全部 gitignored（規則見根目錄 `.gitignore`）。
+
+## 內含物件
+
+| 檔案 | git | 用途 |
+|---|---|---|
+| `README.md` | ✅ committed | 本說明 |
+| `run-STPViewer.ps1.example` | ✅ committed | Windows 啟動腳本範本 |
+| `run-STPViewer.sh.example` | ✅ committed | Git Bash 啟動腳本範本 |
+| `run-STPViewer.ps1` / `.sh` | 🚫 ignored | 從範本複製後的本機實值版 |
+
+> STPViewer 為離線桌面工具，目前**沒有任何 DB 密碼 / ApiKey**；
+> 腳本僅做 build + run。未來若加入需要 secret 的功能（雲端授權、回報伺服器等），
+> 依範本內註解加上 env var 注入。
+
+## 第一次使用
+
+```powershell
+cd secret
+Copy-Item run-STPViewer.ps1.example run-STPViewer.ps1
+.\run-STPViewer.ps1
+```