feat(plotly): opstool-style contour, loads, supports, ghost and animation

Bring the Plotly canvas in line with opstool's visualisation recipes.

Camera / interaction:
- frame the camera in plotly's normalized scene units, using the model
  bounds (grid excluded); a data-unit eye rendered the model as a speck
- use turntable dragmode so Z stays up and the horizon stays level
- align mouse bindings with the PyVista/VTK backend and document them in
  Help → Mouse Controls

Visualisation:
- colour deformed / modal shapes by response with a shared colourbar
- scale load arrows by |F|, tint per load pattern, hover the magnitude,
  and fix cones rendering as oversized fins (sizemode scaled, not absolute)
- draw DOF-accurate support glyphs (ported from opstool; see NOTICE)
- add an undeformed-reference overlay on both canvas backends
- play mode shapes with plotly frame animation in-page

Tests: builder unit tests plus GUI regression tests for gestures, the
deformed push, the undeformed reference and animation payloads.

tests/gui/test_main_window.py

@@ -39,3 +39,21 @@ def test_close_dirty_hidden_window_does_not_block(qtbot) -> None:  # type: ignor
     assert not window.isVisible()
     assert window.close() is True
     assert window._vm.is_dirty  # unchanged: the prompt was skipped
+
+
+@pytest.mark.gui
+def test_mouse_controls_dialog_is_wired_and_reused(qtbot) -> None:  # type: ignore[no-untyped-def]
+    from otko.views.dialogs.mouse_controls import MouseControlsDialog
+    from otko.views.main_window import MainWindow
+
+    window = MainWindow()
+    qtbot.addWidget(window)
+
+    window._on_mouse_controls()
+    dialog = window._mouse_controls_dialog
+    assert isinstance(dialog, MouseControlsDialog)
+    assert dialog.windowTitle() == "Mouse Controls"
+
+    # Raising the action again reuses the same modeless window.
+    window._on_mouse_controls()
+    assert window._mouse_controls_dialog is dialog