Initial commit: multi-platform emulator with PS1 support

Jetpack Compose app with adaptive layouts (phone/tablet/foldable) using
Window Size Classes. Integrates a C++ libretro frontend via JNI for
actual PS1 emulation using pcsx_rearmed, with AAudio output and
ANativeWindow rendering.

- Emulation core architecture with interface for NES, SNES, N64,
  Genesis, PS1, PS2 (PS1 implemented, others placeholder)
- Touch controller overlay with D-pad (diagonal support), face buttons,
  shoulders, and analog sticks
- Bluetooth/USB controller detection and input mapping
- Customizable controller layout editor with drag-to-reposition
- Game library with auto-scan of /sdcard/Games/ subfolders
- Auto-import of libretro core .so from /sdcard/Games/cores/
- Save states and SRAM persistence

app/src/main/cpp/libretro_frontend.h

@@ -0,0 +1,113 @@
+#pragma once
+
+#include "libretro.h"
+#include "audio_engine.h"
+
+#include <android/native_window.h>
+#include <atomic>
+#include <mutex>
+#include <string>
+#include <thread>
+#include <unordered_map>
+
+class LibretroFrontend {
+public:
+    static LibretroFrontend& instance();
+
+    bool loadCore(const char* soPath);
+    bool loadGame(const char* romPath);
+    void start();
+    void pause();
+    void resume();
+    void stop();
+    void reset();
+
+    void setWindow(ANativeWindow* window);
+    void releaseWindow();
+
+    void setButtonState(uint16_t state);
+    void setAnalogState(int stick, int16_t x, int16_t y);
+
+    bool saveState(const char* path);
+    bool loadState(const char* path);
+
+    void setAudioEnabled(bool enabled);
+    void setFrameSkip(int skip);
+
+    void setSystemDir(const char* dir);
+    void setSaveDir(const char* dir);
+
+    bool isRunning() const { return running_.load(); }
+
+private:
+    LibretroFrontend() = default;
+    ~LibretroFrontend();
+
+    void runLoop();
+    void unloadCore();
+
+    // Libretro callbacks (static because libretro uses C function pointers)
+    static bool environmentCallback(unsigned cmd, void* data);
+    static void videoRefreshCallback(const void* data, unsigned width, unsigned height, size_t pitch);
+    static size_t audioSampleBatchCallback(const int16_t* data, size_t frames);
+    static void audioSampleCallback(int16_t left, int16_t right);
+    static void inputPollCallback();
+    static int16_t inputStateCallback(unsigned port, unsigned device, unsigned index, unsigned id);
+    static void logCallback(enum retro_log_level level, const char* fmt, ...);
+
+    // Core function pointers (resolved via dlsym)
+    void* core_handle_ = nullptr;
+
+    retro_init_t                     core_init_ = nullptr;
+    retro_deinit_t                   core_deinit_ = nullptr;
+    retro_api_version_t              core_api_version_ = nullptr;
+    retro_get_system_info_t          core_get_system_info_ = nullptr;
+    retro_get_system_av_info_t       core_get_system_av_info_ = nullptr;
+    retro_set_environment_t          core_set_environment_ = nullptr;
+    retro_set_video_refresh_t        core_set_video_refresh_ = nullptr;
+    retro_set_audio_sample_t         core_set_audio_sample_ = nullptr;
+    retro_set_audio_sample_batch_t   core_set_audio_sample_batch_ = nullptr;
+    retro_set_input_poll_t           core_set_input_poll_ = nullptr;
+    retro_set_input_state_t          core_set_input_state_ = nullptr;
+    retro_set_controller_port_device_t core_set_controller_port_device_ = nullptr;
+    retro_load_game_t                core_load_game_ = nullptr;
+    retro_unload_game_t              core_unload_game_ = nullptr;
+    retro_run_t                      core_run_ = nullptr;
+    retro_reset_t                    core_reset_ = nullptr;
+    retro_serialize_size_t           core_serialize_size_ = nullptr;
+    retro_serialize_t                core_serialize_ = nullptr;
+    retro_unserialize_t              core_unserialize_ = nullptr;
+    retro_get_memory_data_t          core_get_memory_data_ = nullptr;
+    retro_get_memory_size_t          core_get_memory_size_ = nullptr;
+
+    // State
+    std::atomic<bool> running_{false};
+    std::atomic<bool> paused_{false};
+    std::atomic<bool> game_loaded_{false};
+    std::thread emu_thread_;
+
+    // Video
+    ANativeWindow* window_ = nullptr;
+    std::mutex window_mutex_;
+    unsigned pixel_format_ = RETRO_PIXEL_FORMAT_RGB565;
+
+    // Audio
+    AudioEngine audio_engine_;
+
+    // Input
+    std::atomic<uint16_t> button_state_{0};
+    std::atomic<int16_t> analog_lx_{0}, analog_ly_{0};
+    std::atomic<int16_t> analog_rx_{0}, analog_ry_{0};
+
+    // Paths
+    std::string system_dir_;
+    std::string save_dir_;
+
+    // Frame timing
+    double target_fps_ = 60.0;
+    int frame_skip_ = 0;
+
+    // Core options
+    std::unordered_map<std::string, std::string> core_options_;
+    std::atomic<bool> options_updated_{false};
+};