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.h

@@ -0,0 +1,37 @@
+// Copyright 2025 Pound Emulator Project. All rights reserved.
+#pragma once
+
+#include "../Panel.h"
+#include <deque>
+#include <chrono>
+
+namespace Pound::GUI
+{
+
+    class PerformancePanel : public Panel
+    {
+    public:
+        PerformancePanel();
+
+        void Render() override;
+        void Update();
+
+    private:
+        struct PerformanceData
+        {
+            float fps = 0.0f;
+            float frame_time = 0.0f;
+            float cpu_usage = 0.0f;
+            float memory_usage = 0.0f;
+        };
+
+        PerformanceData current_data;
+        std::deque<float> fps_history;
+        std::deque<float> frame_time_history;
+        static constexpr size_t HISTORY_SIZE = 120;
+
+        std::chrono::steady_clock::time_point last_update;
+        int frame_count = 0;
+    };
+
+} // namespace Pound::GUI