feat(map): add peak highlights and live metrics to PNG export

- Draw rings around hottest and coldest sensors on export.
- Extend export_image to support second line for live metrics.
- Format detailed sensor stats in export footer.
- Add test coverage for footer rows, overlays, and stats.

src/pygui/ISC/Tabs/components/StreamControlPanel.qml

@@ -15,7 +15,7 @@ Rectangle {
     border.color: Theme.sideBorder
     border.width: 1
 
-    signal exportRequested(string filePath)
+    signal exportRequested(string filePath, string extra)
 
     property int _liveSecs: 0
     Connections {
@@ -310,7 +310,14 @@ Rectangle {
                 nameFilters: ["PNG files (*.png)"]
                 onAccepted: {
                     var path = String(selectedFile).replace(/^file:\/\//, "");
-                    root.exportRequested(path);
+                    var extra = "";
+                    if (streamController.mode === "live") {
+                        extra = "Frames: " + streamController.receivedCount
+                              + "   Errors: " + streamController.errorCount
+                              + "   Resyncs: " + streamController.resyncCount
+                              + "   Elapsed: " + root.fmtTime(root._liveSecs);
+                    }
+                    root.exportRequested(path, extra);
                 }
             }
         }