final review fixes: reject inf plot width, nearest-cell distance in double, tour wording

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

src/layout_store.cpp

@@ -4,6 +4,7 @@
 #include "layout_store.hpp"
 
 #include <algorithm>
+#include <cmath>
 #include <cstdint>
 #include <cstdio>
 #include <cstdlib>
@@ -619,7 +620,7 @@ bool load_layout(const std::string& path, LayoutState& out) {
         }
       } else if (key == "width") {
         const double w = std::strtod(value.c_str(), nullptr);
-        if (w > 0.0) st.rows.back().width = w;
+        if (std::isfinite(w) && w > 0.0) st.rows.back().width = w;
       }
     } else if (section == Section::Math && !st.math.empty()) {
       MathChannel& m = st.math.back();

src/ui_tour.cpp

@@ -442,7 +442,7 @@ struct TourStep {
 constexpr TourStep kTourSteps[] = {
     {"plot", nullptr, "The plot",
      "Every signal you have switched on is drawn here, all plots sharing one time axis. The wheel "
-     "zooms, a drag pans, and a right-click on a row opens that plot's own menu.",
+     "zooms, a drag pans, and a right-click on a plot opens that plot's own menu.",
      &App::area_overlay},
     {"badges", nullptr, "The badges",
      "Setup is reached by the thing it configures. A badge per signal opens that signal's colour, "