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/tests/test_ui_smoke.py

@@ -920,6 +920,11 @@ def test_depth_view_reports_missing_data_and_fixes_its_scale(make_window):
     window._on_run_tick()
     latched = window.arrow_panel.depth_scale_label.text()
     assert latched
+    shared = window.mesh3d_panel._shared_depth_scale
+    assert shared == window._depth_range_value
+    assert shared is not None
+    assert shared[0] == pytest.approx(0.0)
+    assert shared[1] == pytest.approx(1.0)
 
     window._last_rendered_view_mode = None
     stuck.emit(ui_check._fake_packet(2, depth=np.linspace(0.0, 9.0, 64).reshape(8, 8)))
@@ -927,6 +932,9 @@ def test_depth_view_reports_missing_data_and_fixes_its_scale(make_window):
     assert window.arrow_panel.depth_scale_label.text() == latched, (
         "the depth colour scale re-fitted on every frame"
     )
+    assert window.mesh3d_panel._shared_depth_scale == shared, (
+        "the 3D depth colour span must stay locked to the 2D latch"
+    )
     _finish(window, stuck)