feat: add C++ ImGui functions for core UI and visualization

Funciones C++/ImGui para dashboards (grid, panel, docking, sidebar, tabs),
visualizaciones (candlestick, gauge, histogram, pie, sparkline, heatmap,
scatter, line, bar, surface3d, kpi, table), grafos (force layout, renderer,
viewport, spatial hash, types) y utilidades (time series buffer, tracy zones,
memory/fps overlay, plot theme).

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

cpp/functions/core/sidebar.cpp

@@ -0,0 +1,25 @@
+#include "core/sidebar.h"
+#include "imgui.h"
+
+static bool s_sidebar_was_open = false;
+
+bool sidebar_begin(const char* title, bool* open, float width) {
+    if (!*open) {
+        s_sidebar_was_open = false;
+        if (ImGui::Button(">")) {
+            *open = true;
+        }
+        return false;
+    }
+
+    s_sidebar_was_open = true;
+    ImGui::SetNextWindowSize(ImVec2(width, 0.0f), ImGuiCond_Always);
+    ImGui::Begin(title, open, ImGuiWindowFlags_NoCollapse);
+    return true;
+}
+
+void sidebar_end() {
+    if (s_sidebar_was_open) {
+        ImGui::End();
+    }
+}