fix Studio reset, 3D base colour and arrow-trigger defects

The tracker reset was decided by which panel was on screen rather than by the
session, the automatic colour range moved the 3D surface's base colour on the first
press, and the 2D canvas and the 3D overlay applied different flow thresholds (622
arrows against 432 on a real recording). ui_check 600/0; apps/studio 380 items and
shared 390 items with no failures; real-GL 18 items, only the pre-existing
colour-scale failure; AutoCal 358 passed; both views now select identical arrows on
all 42 frames of a real video.

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

@@ -468,13 +468,18 @@ class ToolbarWidget(QWidget):
         The window calls this to *state* what the session is doing (a replay began,
         a session ended, a recompute pass stopped). An operator's own click goes
         through the button instead, and is routed by ``_on_run_toggled``.
+
+        Reset is left alone here for the same reason ``_on_run_toggled`` leaves it
+        alone: unchecked means "paused" as often as it means "stopped", and a paused
+        session still owns its device. Whether the tracker can be zeroed is the
+        session's answer (``StudioMainWindow._update_run_enabled``), not this
+        control's, so a view switch that merely states the transport cannot take a
+        device action away.
         """
         self.btn_run.blockSignals(True)
         self.btn_run.setChecked(bool(checked))
         self.btn_run.blockSignals(False)
         self.refresh_labels()
-        if not checked:
-            self.btn_reset.setEnabled(False)
 
     def set_stop_enabled(self, enabled: bool) -> None:
         """Stop is offered for as long as there is something to end.