统一 2D/3D 深度色条为同一量程。

将 2D 闩锁的深度色彩区间推给 3D 自动着色，固定量程仍跟旋钮。用 test_shared_depth_scale 与深度闩锁冒烟用例验证。

apps/studio/src/orisys_studio/ui/mesh3d_panel.py

@@ -114,6 +114,8 @@ class Mesh3dPanel(QFrame):
         #: The session's island latch, shared with the 2D canvas (see
         #: ``set_domain_latch``). Held until the view exists.
         self._domain_latch = None
+        #: The 2D canvas's latched depth colour span (see ``set_shared_depth_scale``).
+        self._shared_depth_scale: tuple[float, float] | None = None
 
         # Reserve this top-level window's native handle *now*, before the window is
         # shown and while no OpenGL widget exists yet.
@@ -227,6 +229,12 @@ class Mesh3dPanel(QFrame):
         if self._view is not None and hasattr(self._view, "set_theme"):
             self._view.set_theme(self._theme)
 
+    def set_shared_depth_scale(self, span: tuple[float, float] | None) -> None:
+        """Share the 2D depth colour span with the 3D surface (and hold it until built)."""
+        self._shared_depth_scale = None if span is None else (float(span[0]), float(span[1]))
+        if self._view is not None and hasattr(self._view, "set_shared_depth_scale"):
+            self._view.set_shared_depth_scale(self._shared_depth_scale)
+
     def set_domain_latch(self, latch) -> None:
         """Share the 2D canvas's island latch with the 3D pane (see ``Scene3DView``).
 
@@ -321,6 +329,8 @@ class Mesh3dPanel(QFrame):
             view.set_theme(self._theme)
         if self._domain_latch is not None and hasattr(view, "set_domain_latch"):
             view.set_domain_latch(self._domain_latch)
+        if hasattr(view, "set_shared_depth_scale"):
+            view.set_shared_depth_scale(self._shared_depth_scale)
         if self._pending_settings is not None:
             view.restore_settings(self._pending_settings)
         # The kind was decided before the view existed (the window sets it when the