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

platformio.ini

@@ -0,0 +1,20 @@
+; PlatformIO project configuration
+; ESP32-S3 Loopy Pro Launchpad-Compatible Foot Controller
+
+[env:esp32s3]
+platform = espressif32
+board = esp32-s3-devkitc-1
+framework = arduino
+
+; USB settings for MIDI
+build_flags =
+    -DARDUINO_USB_MODE=1
+    -DARDUINO_USB_CDC_ON_BOOT=1
+    -DUSE_TINYUSB
+
+; Serial monitoring
+monitor_speed = 115200
+
+; Partition scheme with more space
+board_build.partitions = default_8MB.csv
+board_build.arduino.memory_type = qio_opi