Guard poll() against a mode-apply mid-flight; two doc corrections

Extends the OnTimer guard to skip session.poll() itself while modeApplyInProgress(), preventing an undo/redo or project-switch reload from replacing the view model under an in-flight applyMode.

src/shell/view/view.cpp

@@ -271,6 +271,7 @@ std::vector<LaneTrack> readLaneTracks(
     std::vector<LaneTrack> tracks;
     tracks.reserve(handleByGuid.size());
     for (const auto& [guid, tr] : handleByGuid) {
+        if (!tr) continue;  // TrackHandles legally carries nulls post-validation (view.cpp)
         LaneTrack lt;
         lt.trackGuid = guid;