fix(editor): euler display precision at gimbal lock (90 -> 89.98)

Typing 90 degrees on the pitch axis showed 89.98. The stored quat is
exact (matrices differ by 0.0) -- the noise is display-side: quat's
sin(90) components square to 0.99999994 in float, and asin() diverges
at |sin|->1, amplifying 6e-8 into 0.02 degrees. Yaw/roll use atan2 and
were always exact, matching the user's report being X-axis only.

Two fixes, both aligned with how UE gets away with it (internally UE
is quat + equally pathological, its Details panel just shows one
decimal):
- GetRotation gimbal-lock threshold 1.0 -> 1-1e-6: pitch near +-90
  now takes the composite-angle atan2 branch (ratio-stable) instead
  of asin, so typing 90.0 reads back exactly 90.0. Probed: X=90 and
  X=-90 now round-trip to 0 error; generic poses stay ~1e-6 deg.
- Rotation row shows one decimal ("%.1f", UE Details default), masking
  the residual asin noise for angles near (not at) the pole; Ctrl+Click
  input stays full precision. Negative zero from atan2 cleaned up.

Remaining asin noise for e.g. 89.9 (~9e-4 deg) is below the 1-decimal
display and unreachable in practice.

App/editor/InspectorPanel.cpp

@@ -73,9 +73,12 @@ namespace
 
     // UE 风变换行：label + 三轴色 DragFloat（轴色对齐 Gizmo：X 红 /
     // Y 绿 / Z 蓝）。拖拽粗调；Ctrl+Click 进输入框键入精确值。
-    // 任一轴变化返回 true
+    // 任一轴变化返回 true。fmt = 显示格式（旋转行传 "%.1f" 对齐
+    // UE Details 默认 1 位小数——欧拉显示端有固有反解噪声，见
+    // TransformComponent::GetRotation 注释）
     bool DragVec3Row(const char* label, glm::vec3& v, float speed,
-                     float mn = -3.4e38f, float mx = 3.4e38f)
+                     float mn = -3.4e38f, float mx = 3.4e38f,
+                     const char* fmt = "%.2f")
     {
         ImGui::TextUnformatted(label);
         ImGui::SameLine(72.0f);   // 固定标签列宽 → 三行输入框对齐
@@ -97,7 +100,7 @@ namespace
             ImGui::SetNextItemWidth(boxW);
             changed |= ImGui::DragFloat(
                 i == 0 ? "##x" : i == 1 ? "##y" : "##z",
-                &v[i], speed, mn, mx, "%.2f");
+                &v[i], speed, mn, mx, fmt);
             ImGui::PopStyleColor();
             if (i < 2) ImGui::SameLine();
         }
@@ -213,7 +216,13 @@ void InspectorPanel::Draw(const EditorContext& ctx, entt::entity selected)
                 t->SetPosition(pos);
             }
             glm::vec3 rot = t->GetRotation();   // 派生欧拉（度）
-            if (DragVec3Row("rotation", rot, 0.5f))
+            for (int i = 0; i < 3; ++i)
+            {
+                if (rot[i] == 0.0f) rot[i] = 0.0f;   // 清 -0.0（atan2 副产物）
+            }
+            // "%.1f" = UE Details 默认显示精度（反解噪声 ~0.02° @ pitch 90°，
+            // 存储端 quat 精确；手输 Ctrl+Click 仍全精度写入）
+            if (DragVec3Row("rotation", rot, 0.5f, -3.4e38f, 3.4e38f, "%.1f"))
             {
                 t->SetRotation(rot);
             }

Engine/include/Engine/ECS/Components.h

@@ -65,7 +65,12 @@ namespace Engine::ECS {
         {
             const glm::mat3 R = glm::mat3_cast(m_Rotation);
             const f32 sp = std::clamp(-R[2][1], -1.0f, 1.0f);   // = sin(pitch)
-            if (std::abs(sp) < 1.0f) {
+            // 万向锁分支阈值 1e-6：asin 在 |sin|→1 处导数发散（sin90 的
+            // float 表示差 6e-8 → asin 放大成 0.02° 显示噪声，用户实测
+            // 90 → 89.98）。贴锁区改走组合角 atan2（分子分母同源缩放，
+            // 比值稳定）→ 手输 90.0 显示 90.0。落入该窄区（±0.00057°）
+            // 的真实 yaw/roll 被归并为组合角，UI 输入不可达，可接受
+            if (std::abs(sp) < 1.0f - 1e-6f) {
                 return glm::degrees(glm::vec3(
                     std::asin(sp),
                     std::atan2(R[2][0], R[2][2]),