Implemented new C++ logic

Client/streamhub/SourcePanel.h

@@ -0,0 +1,17 @@
+/**
+ * @file SourcePanel.h
+ * @brief Left sidebar: source tree with draggable signal leaves.
+ */
+
+#pragma once
+
+namespace StreamHubClient {
+class App;
+
+/**
+ * @brief Render the source browser sidebar.
+ * Must be called inside an ImGui child window.
+ */
+void RenderSourcePanel(App& app);
+
+} /* namespace StreamHubClient */