Fix for ESP32-S3-WROOM-1: safe GPIO pins, serial flush, delays

- Switch pins: 2-7, 15-18 (avoids USB 19/20, PSRAM 26-32, JTAG 34-37)
- LED pins: 38-42, 45-48, 21 (high GPIOs, no special functions)
- Add Serial.flush() after init messages
- Increase startup delays for reliable serial output
- Board: esp32-s3-devkitc-1-n16r8

src/led_stub.cpp

@@ -2,7 +2,7 @@
 #include <Arduino.h>
 
 static const uint8_t LED_PINS[10] = {
-    11, 12, 13, 14, 15, 16, 17, 18, 19, 20
+    38, 39, 40, 41, 42, 45, 46, 47, 48, 21
 };
 
 DefaultLedStub::DefaultLedStub() : initialized(false) {
@@ -22,21 +22,23 @@ void DefaultLedStub::begin() {
     }
     initialized = true;
 
-    Serial.println("[LED] Startup colour cycle...");
+    Serial.println("[LED] Startup animation...");
 
     for (int i = 0; i < NUM_LEDS; i++) {
         digitalWrite(LED_PINS[i], HIGH);
-        Serial.printf("[LED] LED %d ON (GPIO %d)\n", i, LED_PINS[i]);
+        Serial.printf("[LED] LED %d ON  (GPIO %d)\n", i, LED_PINS[i]);
+        delay(150);
+    }
+
+    delay(300);
+
+    for (int i = NUM_LEDS - 1; i >= 0; i--) {
+        digitalWrite(LED_PINS[i], LOW);
+        Serial.printf("[LED] LED %d OFF (GPIO %d)\n", i, LED_PINS[i]);
         delay(100);
     }
 
-    for (int i = 0; i < NUM_LEDS; i++) {
-        digitalWrite(LED_PINS[i], LOW);
-        delay(50);
-    }
-
-    clear_all();
-    Serial.println("[LED] Startup cycle complete");
+    Serial.println("[LED] Startup complete");
 }
 
 void DefaultLedStub::set_led_state(uint8_t note, uint8_t channel, uint8_t velocity) {
@@ -57,7 +59,7 @@ void DefaultLedStub::set_led_state(uint8_t note, uint8_t channel, uint8_t veloci
                       note, led_index, channel, velocity,
                       velocity > 0 ? "ON" : "OFF");
     } else {
-        Serial.printf("[LED] Index out of range: %d (Note: %d)\n", led_index, note);
+        Serial.printf("[LED] Out of range: %d (Note: %d)\n", led_index, note);
     }
 }
 
@@ -69,5 +71,5 @@ void DefaultLedStub::clear_all() {
             digitalWrite(LED_PINS[i], LOW);
         }
     }
-    Serial.println("[LED] All LEDs cleared");
+    Serial.println("[LED] All cleared");
 }