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

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;
+}