Convert to PlatformIO/Arduino format

- Replace ESP-IDF structure with PlatformIO (platformio.ini)
- Move source files to src/ and include/
- Move libraries to lib/ directory
- Replace FreeRTOS with Arduino task/vTaskDelay
- Use Arduino MIDI library instead of raw TinyUSB
- Dual-core: MIDI on core 0, controller on core 1

include/app_task.h

@@ -0,0 +1,33 @@
+#pragma once
+
+#include <cstdint>
+#include "midi_transport.h"
+#include "led_stub.h"
+#include "switch_stub.h"
+
+struct PadMapping {
+    uint8_t physical_switch;
+    uint8_t midi_channel;
+    uint8_t midi_note;
+    uint8_t led_index;
+};
+
+class AppTask {
+public:
+    AppTask(LedStub* led, SwitchStub* sw, UsbMidiTransport* midi);
+    
+    void begin();
+    void update();
+    
+private:
+    LedStub* led_driver;
+    SwitchStub* switch_driver;
+    UsbMidiTransport* midi_transport;
+    
+    static const uint8_t NUM_PADS = 10;
+    PadMapping pad_mapping[NUM_PADS];
+    bool last_switch_state[NUM_PADS];
+    
+    void process_midi_event(const MidiEvent& event);
+    void process_switch_event(uint8_t switch_id, bool pressed);
+};

include/led_stub.h

@@ -0,0 +1,37 @@
+#pragma once
+
+#include <cstdint>
+
+class LedStub {
+public:
+    virtual ~LedStub() {}
+    
+    virtual void begin() = 0;
+    virtual void set_led_state(uint8_t note, uint8_t channel, uint8_t velocity) = 0;
+    virtual void clear_all() = 0;
+    
+    virtual uint8_t note_to_index(uint8_t note) {
+        return note;
+    }
+};
+
+struct LedState {
+    uint8_t note;
+    uint8_t channel;
+    uint8_t velocity;
+    uint32_t timestamp;
+    bool active;
+};
+
+class DefaultLedStub : public LedStub {
+private:
+    static const uint8_t NUM_LEDS = 10;
+    LedState led_states[NUM_LEDS];
+    bool initialized;
+    
+public:
+    DefaultLedStub();
+    void begin() override;
+    void set_led_state(uint8_t note, uint8_t channel, uint8_t velocity) override;
+    void clear_all() override;
+};

include/midi_transport.h

@@ -0,0 +1,45 @@
+#pragma once
+
+#include <cstdint>
+#include <functional>
+
+struct MidiEvent {
+    enum Type {
+        NOTE_ON,
+        NOTE_OFF,
+        CONTROL_CHANGE,
+        PROGRAM_CHANGE,
+        PITCH_BEND,
+        AFTERTOUCH_POLY,
+        AFTERTOUCH_CHAN,
+        SYSEX
+    } type;
+    
+    uint8_t channel;      // MIDI channel (1-16)
+    uint8_t data1;         // Note number or CC number
+    uint8_t data2;         // Velocity or CC value
+    uint32_t timestamp;   // Event timestamp
+};
+
+class UsbMidiTransport {
+public:
+    UsbMidiTransport();
+    ~UsbMidiTransport();
+    
+    bool begin();
+    void update();
+    
+    // Callback registration
+    void on_midi_receive(std::function<void(const MidiEvent&)> callback);
+    
+    // Send MIDI
+    void send_note_on(uint8_t channel, uint8_t note, uint8_t velocity);
+    void send_note_off(uint8_t channel, uint8_t note, uint8_t velocity);
+    void send_cc(uint8_t channel, uint8_t cc, uint8_t value);
+    
+private:
+    std::function<void(const MidiEvent&)> receive_callback;
+    bool initialized;
+    
+    void parse_midi_packet(const uint8_t* buffer, uint32_t size, MidiEvent& event);
+};

include/switch_stub.h

@@ -0,0 +1,36 @@
+#pragma once
+
+#include <cstdint>
+
+class SwitchStub {
+public:
+    virtual ~SwitchStub() {}
+    
+    virtual void begin() = 0;
+    virtual bool is_pressed(uint8_t switch_id) = 0;
+    virtual void configure_switch(uint8_t switch_id, uint8_t gpio_pin) = 0;
+    virtual void set_debounce_time(uint32_t time_ms) = 0;
+};
+
+struct SwitchState {
+    uint8_t id;
+    uint8_t gpio_pin;
+    bool current_state;
+    bool previous_state;
+    uint32_t last_change_time;
+    uint32_t debounce_time;
+};
+
+class DefaultSwitchStub : public SwitchStub {
+private:
+    static const uint8_t NUM_SWITCHES = 10;
+    SwitchState switch_states[NUM_SWITCHES];
+    bool initialized;
+    
+public:
+    DefaultSwitchStub();
+    void begin() override;
+    bool is_pressed(uint8_t switch_id) override;
+    void configure_switch(uint8_t switch_id, uint8_t gpio_pin) override;
+    void set_debounce_time(uint32_t time_ms) override;
+};