Add miditest and mapping commands for LED layout debugging

include/app_task.h

@@ -18,6 +18,7 @@ public:
     
     void begin();
     void update();
+    void process_midi_event(const MidiEvent& event);  // public for test commands
     
 private:
     LedStub* led_driver;
@@ -28,6 +29,5 @@ private:
     PadMapping pad_mapping[NUM_PADS];
     bool last_switch_state[NUM_PADS];
     
-    void process_midi_event(const MidiEvent& event);
     void process_switch_event(uint8_t switch_id, bool pressed);
 };