Implemented qt port + e2e

Client/streamhub-qt/HistoryBar.h

@@ -0,0 +1,42 @@
+/**
+ * @file HistoryBar.h
+ * @brief History-browsing toolbar: Live, range readout, pan, jump presets, All.
+ *
+ * Operates on the PlotGrid (sets all plots non-live and seeds their stored X
+ * range). Mirrors the ImGui App::renderHistoryBar. Visible only when the hub
+ * reports history is enabled and populated.
+ */
+
+#pragma once
+
+#include <QWidget>
+
+class QLabel;
+
+namespace shq {
+
+class Hub;
+class PlotGrid;
+
+class HistoryBar : public QWidget {
+    Q_OBJECT
+public:
+    HistoryBar(Hub* hub, PlotGrid* grid, QWidget* parent = nullptr);
+
+public Q_SLOTS:
+    /** Update the range readout (called by the 60 Hz tick). */
+    void updateReadout();
+    /** Jump all plots to the full available history range. */
+    void showAll();
+
+Q_SIGNALS:
+    /** User pressed Live → MainWindow hides this bar. */
+    void liveRequested();
+
+private:
+    Hub*      hub_;
+    PlotGrid* grid_;
+    QLabel*   rangeLbl_ = nullptr;
+};
+
+} /* namespace shq */