Fix Launchpad mode MIDI receive and color palette

- Fixed note matching bug: removed channel check so notes 36-45 match
  across channels 1-3 (Launchpad static/flashing/pulsing)
- Simplified LED lookup to match by note only (channel stored for mode)
- Replaced sparse palette with proper RGB gradients between key
  breakpoints (Red, Orange, Yellow, Green, Cyan, Blue, Purple, Off)

src/app_task.cpp

@@ -56,25 +56,23 @@ void AppTask::process_midi_event(const MidiEvent& event) {
     // Notes 36-45 (C2-A2) map to pads 0-9
     // Velocity 1-127 = color palette index
     if (event.type == MidiEvent::NOTE_ON || event.type == MidiEvent::NOTE_OFF) {
-        // Only handle channels 1-3 (Launchpad channels)
         if (midi_channel >= 1 && midi_channel <= 3) {
             for (uint8_t i = 0; i < NUM_PADS; i++) {
-                if (pad_mapping[i].midi_channel == midi_channel && 
-                    pad_mapping[i].midi_note == midi_note) {
+                if (pad_mapping[i].midi_note == midi_note) {
                     led_index = pad_mapping[i].led_index;
                     break;
                 }
             }
-            
+
             if (led_index < NUM_PADS) {
                 uint8_t color_vel = (event.type == MidiEvent::NOTE_ON) ? midi_velocity : 0;
-                
+
                 led_driver->set_led_state(
-                    pad_mapping[led_index].midi_note,
-                    pad_mapping[led_index].midi_channel,
+                    midi_note,
+                    midi_channel,
                     color_vel
                 );
-                
+
                 Serial.printf("[APP] NOTE -> LED: Ch%d Note%d Vel%d -> LED%d\n",
                               midi_channel, midi_note, color_vel, led_index);
             } else {