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/candlestick.h

@@ -0,0 +1,9 @@
+#pragma once
+
+// Renders an OHLC candlestick chart using ImPlot custom rendering.
+// Call within an ImGui frame (inside fn::run_app render callback).
+// Green candles when close >= open, red when close < open.
+// width_percent controls candle body width as a fraction of inter-candle spacing.
+void candlestick(const char* title, const double* dates, const double* opens,
+                 const double* closes, const double* lows, const double* highs,
+                 int count, float width_percent = 0.25f, bool tooltip = true);