feat(ui): Add gizmo manipulator for axis move/rotate (v0.3.0)

- New "操作器" toggle: select a file in the tree and a 3-axis gizmo
  appears at its center -- XYZ arrows (TranslateManipulator) to move
  along an axis regardless of view angle, and rotation rings
  (RotateManipulator) to rotate any angle about an axis
- Manipulators bind to a proxy ModelVisual3D; the proxy's transform
  is mirrored to all target BodyVisuals during drag (GPU-side, temp)
- On release the accumulated transform is baked into B-rep via
  TransformRoot (deferred with Dispatcher.BeginInvoke to avoid
  reentrancy with the manipulator's own mouse-up handling); the
  gizmo re-centers on the new bounds
- Temporary transforms are cleared with Transform3D.Identity, never
  null (HelixToolkit GetTransform crashes on null child.Transform)
- Selecting another file retargets the gizmo; removing the target
  hides it
- Docs updated (ARCHITECTURE Phase 10, CLAUDE.md, README)

Known limitation: gizmo handles are occluded inside solid parts
(WPF single depth buffer). Next: always-on-top overlay viewport.

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

CLAUDE.md

@@ -44,7 +44,12 @@ dotnet publish src/STPViewer -c Release -o publish/STPViewer
   合併網格的 hit-test 走 `_mergedMap`（合併 Model → leaf）；拖曳中邊線用 `_edgesSuspended` 暫停
 - ⚠️ **`Visual3D.Transform` 永遠不要設成 `null`，清除要用 `Transform3D.Identity`**。HelixToolkit `Viewport3DHelper.GetTransform`
   對 `child.Transform` 沒做 null 檢查（`GeneralTransform3DGroup.Children.Add(null)` → 拋「無法新增空值到集合中」），
-  之後任何 `FindHits` 都會 crash。v0.2.1 修的就是拖曳放開時把 BodyVisual.Transform 設 null（拖過一次後再點擊就炸）
+  之後任何 `FindHits` 都會 crash。v0.2.1 修的就是拖曳放開時把 BodyVisual.Transform 設 null（拖過一次後再點擊就炸）。
+  Gizmo 的暫時 Transform 清除同理一律用 Identity
+- Gizmo 操作器：Helix `TranslateManipulator`/`RotateManipulator` ×6 `Bind` 到代理 `ModelVisual3D`，
+  代理 Transform 變更（`DependencyPropertyDescriptor.AddValueChanged`）即時套到目標 BodyVisual（暫時）；
+  **放開滑鼠才 `TransformRoot` 烘焙** — MouseUp 被 manipulator 標 handled，MainWindow 用 `AddHandler(..., handledEventsToo: true)` 才收得到。
+  烘焙用 `Dispatcher.BeginInvoke` 延後到 manipulator 自身事件處理完，避免 reentrancy；`_gizmoBaking` 旗標防 Transform 歸零的回呼重入
 - 干涉/面距/對齊等運算在背景執行緒；`Freeze()` 幾何後才跨執行緒
 - 匯入在背景執行緒；`Freeze()` 幾何後才跨執行緒
 - Commit 格式：Conventional Commits（`feat:` / `fix:` / `docs:` …）