editor: revert self-drawn scale gizmo, clip degenerate axes instead

User feedback: the self-drawn scale handles clash visually with the
ImGuizmo translate/rotate rods (different size/style, clearly not one
widget). Keep the library widget for all three ops for visual
consistency and prevent mis-drags by masking degenerate axes via
SetAxisMask:

- translate: axis ~ parallel to camera-to-object line (sin < 0.25)
- scale: axis ~ perpendicular to camera-to-object line (|dot| < 0.1,
  intersection numerator identically zero -> grab fails/values jump)
  OR axis ~ parallel to view direction (|dot| > 0.98, zero screen
  displacement -> value never changes)
- rotate: screen-space math, no degeneracy, no mask

Masked axes are neither drawn nor activatable; a slight view change
restores them. Center uniform-scale square (MT_SCALE_XYZ, pure screen
space) stays available in any view.

App/editor/ViewportPanel.h

@@ -35,21 +35,7 @@ struct GizmoState {
     int op = 7;             // ImGuizmo::TRANSLATE（TRANSLATE_X|Y|Z）
     bool localSpace = true; // 操纵空间：true=模型轴（旋转/缩放语义），
                             // T 键切 world
-    bool dragging = false;  // 拖拽中（IsUsing 或自绘缩放拖拽）→ 鼠标归
-                            // Gizmo 不给游戏侧（Editor::BlockingMouse）
-
-    // ---- 自绘缩放 gizmo（op==SCALE 整体不走 ImGuizmo）----
-    // 库内缩放的 hover/拖拽依赖"法线=轴"平面求交：正对视角（轴⊥
-    // 相机连线）时求交分子恒 0 → 杆抓不到、数值随机猛变；轴∥视线
-    // 时又无屏幕位移。submodule 禁改，AxisMask 只能"藏"不能"补"
-    // → 调用层整体自绘三轴杆 + 中心等比方块（纯屏幕空间数学，任意
-    // 视角良构），实现见 ViewportPanel.cpp ScaleGizmoSelf
-    bool scaleDragActive = false;   // 自绘缩放拖拽中
-    int  scaleDragAxis = -1;        // 拖拽目标：0/1/2 轴；-2 = 中心等比
-    bool scaleHover = false;        // 本帧悬停/拖拽自绘手柄 → 抑制 pick
-    float scaleStartMouse[2] = {0.0f, 0.0f}; // 拖拽起始鼠标（屏幕系）
-    float scaleStartDist = 0.0f;    // 起始鼠标到杆心距离（径向映射用）
-    float scaleStartScale[3] = {1.0f, 1.0f, 1.0f}; // 拖拽起始 scale
+    bool dragging = false;  // 拖拽中（IsUsing）→ 鼠标归 Gizmo 不给游戏侧
 };
 
 class ViewportPanel {