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.h

@@ -0,0 +1,14 @@
+#pragma once
+
+// Collapsible sidebar panel.
+// Usage:
+//   if (sidebar_begin("Filters", &sidebar_open)) {
+//       // draw filter controls
+//   }
+//   sidebar_end();
+//
+// The sidebar renders as a fixed-width ImGui window.
+// When collapsed, only a small toggle button is shown.
+
+bool sidebar_begin(const char* title, bool* open, float width = 250.0f);
+void sidebar_end();