feat: add ImGui frontend support with game selection and debug panels

include/panda_sdl/imgui_layer.hpp

@@ -0,0 +1,50 @@
+#pragma once
+
+#ifdef IMGUI_FRONTEND
+
+#include <SDL.h>
+
+#include <functional>
+#include <optional>
+
+#include "emulator.hpp"
+
+class ImGuiLayer {
+  public:
+	ImGuiLayer(SDL_Window* window, SDL_GLContext context, Emulator& emu);
+	void init();
+	void shutdown();
+	void processEvent(const SDL_Event& event);
+	void beginFrame();
+	void render();
+	void handleHotkey(const SDL_Event& event);
+	std::optional<std::filesystem::path> runGameSelector();
+
+	bool wantsCaptureKeyboard() const { return captureKeyboard; }
+	bool wantsCaptureMouse() const { return captureMouse; }
+
+	void setPaused(bool paused) { isPaused = paused; }
+	void setPauseCallback(std::function<void(bool)> callback) { onPauseChange = std::move(callback); }
+	void setVsyncCallback(std::function<void(bool)> callback) { onVsyncChange = std::move(callback); }
+
+  private:
+	void drawDebugPanel();
+	void drawPausePanel();
+	void drawSettingsPanel();
+
+	SDL_Window* window = nullptr;
+	SDL_GLContext glContext = nullptr;
+	Emulator& emu;
+
+	bool showDebug = true;
+	bool showPauseMenu = false;
+	bool showSettings = false;
+	bool isPaused = false;
+	bool captureKeyboard = false;
+	bool captureMouse = false;
+
+	std::function<void(bool)> onPauseChange;
+	std::function<void(bool)> onVsyncChange;
+};
+
+#endif