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/viz/pie_chart.h

@@ -0,0 +1,7 @@
+#pragma once
+
+// Renders a pie or donut chart using ImPlot::PlotPieChart.
+// Call within an ImGui frame.
+// radius == 0: auto (0.4). radius > 0: explicit radius. radius < 0: donut mode (|radius| as outer, 0.2 as inner).
+void pie_chart(const char* title, const char* const* labels, const float* values, int count, float radius = 0.0f);
+void pie_chart(const char* title, const char* const* labels, const double* values, int count, double radius = 0.0);