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/graph_viewport.h

@@ -0,0 +1,50 @@
+#pragma once
+#include "imgui.h"
+
+struct GraphData;
+struct GraphRenderer;
+struct SpatialHash;
+
+// Persistent state for graph_viewport widget. Create one per viewport and keep
+// alive across frames.
+struct GraphViewportState {
+    // Camera
+    float cam_x = 0.0f, cam_y = 0.0f;
+    float zoom     = 1.0f;
+    float zoom_min = 0.01f, zoom_max = 50.0f;
+
+    // Interaction result (read after calling graph_viewport each frame)
+    int  hovered_node  = -1;   // node index under cursor, -1 if none
+    int  selected_node = -1;   // last clicked node index, -1 if none
+    bool is_dragging   = false;
+
+    // Layout
+    bool  layout_running = true;  // animate force layout each frame
+    float layout_energy  = 0.0f; // kinetic energy from last step
+
+    // Internal — managed by graph_viewport / graph_viewport_destroy
+    GraphRenderer* renderer  = nullptr;
+    SpatialHash*   spatial   = nullptr;
+    bool           initialized = false;
+
+    // Widget pixel dimensions tracked for resize detection
+    int render_w = 0, render_h = 0;
+
+    // Node being dragged (-1 = none)
+    int drag_node = -1;
+};
+
+// Main viewport widget. Call every ImGui frame.
+// id:    unique ImGui widget identifier
+// graph: mutable graph data (node positions updated on drag)
+// state: persistent state (camera, selection, GPU renderer); must outlive frames
+// size:  widget size in pixels — ImVec2(0,0) uses all available space
+// Returns true if any user interaction occurred (hover, click, drag, zoom).
+bool graph_viewport(const char* id, GraphData& graph, GraphViewportState& state,
+                    ImVec2 size = ImVec2(0.0f, 0.0f));
+
+// Release GPU resources. Call once when done with the viewport.
+void graph_viewport_destroy(GraphViewportState& state);
+
+// Fit camera to current graph bounds with 10% padding.
+void graph_viewport_fit(GraphData& graph, GraphViewportState& state);