feat(gui): Extract and modularize GUI system from main.cpp

- Create modular GUI architecture with base Panel class
- Implement GUIManager to handle window lifecycle and panel management
- Add Window wrapper class for SDL3/OpenGL context management
- Create specialized panels:
  - ConsolePanel: Colored log output with timestamps
  - CPUPanel: CPU debugging with tabs for registers, memory, and disassembly
  - PerformancePanel: Real-time FPS and frame time monitoring
- Apply modern dark theme with purple accents
- Add comprehensive menu bar (File, Emulation, View, Tools, Help)
- Update CMakeLists.txt to include new gui/ directory structure
- Refactor main.cpp to use the new GUI system
- Cutom theme on switch colors

gui/panels/PerformancePanel.cpp

@@ -0,0 +1,100 @@
+// Copyright 2025 Pound Emulator Project. All rights reserved.
+
+#include "PerformancePanel.h"
+#include <algorithm>
+
+namespace Pound::GUI
+{
+
+    PerformancePanel::PerformancePanel() : Panel("Performance")
+    {
+        last_update = std::chrono::steady_clock::now();
+    }
+
+    void PerformancePanel::Render()
+    {
+        if (!ImGui::Begin(name.c_str(), &visible))
+        {
+            ImGui::End();
+            return;
+        }
+
+        Update();
+
+        // Performance metrics
+        ImGui::Text("FPS: %.1f", current_data.fps);
+        ImGui::Text("Frame Time: %.2f ms", current_data.frame_time);
+        ImGui::Separator();
+
+        // FPS Graph
+        if (!fps_history.empty())
+        {
+            float fps_array[HISTORY_SIZE];
+            std::copy(fps_history.begin(), fps_history.end(), fps_array);
+
+            ImGui::Text("FPS History:");
+            ImGui::PlotLines("##FPS", fps_array, (int)fps_history.size(), 0, nullptr,
+                             0.0f, 144.0f, ImVec2(0, 80));
+        }
+
+        // Frame Time Graph
+        if (!frame_time_history.empty())
+        {
+            float frame_time_array[HISTORY_SIZE];
+            std::copy(frame_time_history.begin(), frame_time_history.end(), frame_time_array);
+
+            ImGui::Text("Frame Time History (ms):");
+            ImGui::PlotLines("##FrameTime", frame_time_array, (int)frame_time_history.size(), 0, nullptr,
+                             0.0f, 33.33f, ImVec2(0, 80));
+        }
+
+        ImGui::Separator();
+
+        // System info (placeholder)
+        ImGui::Text("CPU Usage: %.1f%%", current_data.cpu_usage);
+        ImGui::Text("Memory Usage: %.1f MB", current_data.memory_usage);
+
+        // Emulation stats
+        ImGui::Separator();
+        ImGui::Text("Emulation Statistics:");
+        ImGui::Text("Instructions/sec: N/A");
+        ImGui::Text("JIT Cache Usage: N/A");
+
+        ImGui::End();
+    }
+
+    void PerformancePanel::Update()
+    {
+        frame_count++;
+
+        auto now = std::chrono::steady_clock::now();
+        auto duration = std::chrono::duration_cast<std::chrono::milliseconds>(now - last_update);
+
+        if (duration.count() >= 100)
+        { // Update every 100ms
+            current_data.fps = frame_count * 1000.0f / duration.count();
+            current_data.frame_time = duration.count() / (float)frame_count;
+
+            fps_history.push_back(current_data.fps);
+            frame_time_history.push_back(current_data.frame_time);
+
+            // Keep history size limited
+            while (fps_history.size() > HISTORY_SIZE)
+            {
+                fps_history.pop_front();
+            }
+            while (frame_time_history.size() > HISTORY_SIZE)
+            {
+                frame_time_history.pop_front();
+            }
+
+            frame_count = 0;
+            last_update = now;
+
+            // TODO: Get actual CPU and memory usage
+            current_data.cpu_usage = 0.0f;
+            current_data.memory_usage = 0.0f;
+        }
+    }
+
+} // namespace Pound::GUI