Add visual MIDI type indicators

- SysEx: ALL LEDs flash white 200ms
- Note: LED 0 flashes red 100ms
- CC: LED 1 flashes green 100ms
- Helps diagnose what MIDI arrives without serial

include/led_stub.h

@@ -12,6 +12,8 @@ public:
     virtual void set_led_brightness(uint8_t brightness) = 0;
     virtual void flash_activity() {}
     virtual void flash_sysex() {}
+    virtual void flash_all(uint8_t r, uint8_t g, uint8_t b, uint16_t duration) {}
+    virtual void flash_one(uint8_t index, uint8_t r, uint8_t g, uint8_t b, uint16_t duration) {}
     virtual void update() {}
     
     virtual uint8_t note_to_index(uint8_t note) {
@@ -49,6 +51,8 @@ public:
     void set_led_brightness(uint8_t brightness) override;
     void flash_activity() override;
     void flash_sysex() override;
+    void flash_all(uint8_t r, uint8_t g, uint8_t b, uint16_t duration) override;
+    void flash_one(uint8_t index, uint8_t r, uint8_t g, uint8_t b, uint16_t duration) override;
     void update() override;
 
     void set_mux(PixelStompMux* mux);

src/app_task.cpp

@@ -46,16 +46,20 @@ void AppTask::process_midi_event(const MidiEvent& event) {
     Serial.printf("[APP] MIDI IN: Type=%d Ch=%d Data1=%d Data2=%d\n",
                   event.type, event.channel, event.data1, event.data2);
 
-    // Flash LED 0 white briefly on ANY MIDI input - visual activity indicator
-    // (visible without serial when connected to iPad)
-    led_driver->flash_activity();
+    // Visual MIDI type indicator (works without serial on iPad)
+    if (event.type == MidiEvent::SYSEX) {
+        led_driver->flash_all(255, 255, 255, 200);  // SysEx = ALL white
+    } else if (event.type == MidiEvent::NOTE_ON || event.type == MidiEvent::NOTE_OFF) {
+        led_driver->flash_one(0, 255, 0, 0, 100);   // Note = LED 0 red
+    } else if (event.type == MidiEvent::CONTROL_CHANGE) {
+        led_driver->flash_one(1, 0, 255, 0, 100);   // CC = LED 1 green
+    }
     
     if (event.type == MidiEvent::SYSEX) {
         // Cin is encoded in channel for SYSEX packets
         uint8_t cin = event.channel;
         uint8_t packet[3] = {event.data1, event.data2, 0};
         process_sysex_packet(packet, cin);
-        led_driver->flash_sysex();
         return;
     }
 

src/led_stub.cpp

@@ -345,3 +345,50 @@ void DefaultLedStub::update() {
         if (heartbeat_phase > 200) heartbeat_phase = 0;
     }
 }
+
+void DefaultLedStub::flash_all(uint8_t r, uint8_t g, uint8_t b, uint16_t duration) {
+    if (!initialized || !mux_ptr) return;
+    
+    // Save all LED states
+    for (int i = 0; i < NUM_LEDS; i++) {
+        if (led_states[i].active) {
+            uint32_t color = launchpad_palette[led_states[i].velocity];
+            sysex_saved_r[i] = (color >> 16) & 0xFF;
+            sysex_saved_g[i] = (color >> 8) & 0xFF;
+            sysex_saved_b[i] = color & 0xFF;
+        } else {
+            sysex_saved_r[i] = 0;
+            sysex_saved_g[i] = 0;
+            sysex_saved_b[i] = 0;
+        }
+    }
+    
+    for (int i = 0; i < NUM_LEDS; i++) {
+        mux_ptr->set_led_color(i, r, g, b);
+    }
+    mux_ptr->show();
+    activity_off_time = millis() + duration;
+    sysex_flash_active = true;
+}
+
+void DefaultLedStub::flash_one(uint8_t index, uint8_t r, uint8_t g, uint8_t b, uint16_t duration) {
+    if (!initialized || !mux_ptr) return;
+    if (index >= NUM_LEDS) return;
+    
+    // Save only this LED's state
+    if (led_states[index].active) {
+        uint32_t color = launchpad_palette[led_states[index].velocity];
+        saved_r = (color >> 16) & 0xFF;
+        saved_g = (color >> 8) & 0xFF;
+        saved_b = color & 0xFF;
+    } else {
+        saved_r = 0;
+        saved_g = 0;
+        saved_b = 0;
+    }
+    
+    mux_ptr->set_led_color(index, r, g, b);
+    mux_ptr->show();
+    activity_off_time = millis() + duration;
+    sysex_flash_active = false;
+}