Move all MIDI processing to Core 0

Move controller.update() inside midi_task on Core 0 to eliminate
TinyUSB cross-core race condition. Previously:
 - Core 1 (loop()): usb_midi.writePacket() in controller.update()
 - Core 0 (midi_task): usb_midi.available()/readPacket()
This race condition causes crashes on button press.

Now:
 - Core 0 (midi_task): midi_transport.update() + controller.update()
 - Core 1 (loop()): led_driver.update() + serial commands only

src/main.cpp

@@ -36,6 +36,7 @@ void midi_task(void* parameter) {
     while (true) {
         midi_transport.update();
         ble_midi_transport.update();
+        controller.update();
         vTaskDelay(1);
     }
 }
@@ -390,7 +391,6 @@ void setup() {
 
 void loop() {
     led_driver.update();
-    controller.update();
 
     if (Serial.available()) {
         String cmd = Serial.readStringUntil('\n');