Fix Phase 1 skeleton: add build system, fix compilation errors

- Add CMakeLists.txt for project and all components
- Add idf_component.yml with TinyUSB dependency
- Create switch_stub.cpp implementation
- Fix app_task.h to match .cpp implementation (2-param signature)
- Fix led_stub.h/cpp class naming (DefaultLedStub)
- Fix midi_transport.cpp TinyUSB API usage (tud_midi_*)
- Move main.cpp to main/ directory
- Add sdkconfig.defaults for ESP32-S3

components/hal/led_stub.h

@@ -1,6 +1,8 @@
-// hal/led_stub.h
+// components/hal/led_stub.h
 #pragma once
 
+#include <cstdint>
+
 class LedStub {
 public:
     virtual ~LedStub() {}
@@ -11,8 +13,6 @@ public:
     
     // Helper function to map MIDI note to LED index
     virtual uint8_t note_to_index(uint8_t note) {
-        // Default implementation - direct mapping
-        // Can be overridden by specific implementations
         return note;
     }
 };
@@ -24,4 +24,18 @@ struct LedState {
     uint8_t velocity;       // Color/brightness (0-127)
     uint32_t timestamp;     // When state was set
     bool active;           // Current on/off state
-};
+};
+
+// Default stub implementation
+class DefaultLedStub : public LedStub {
+private:
+    static const uint8_t NUM_LEDS = 10;
+    LedState led_states[NUM_LEDS];
+    bool initialized;
+    
+public:
+    DefaultLedStub();
+    void begin() override;
+    void set_led_state(uint8_t note, uint8_t channel, uint8_t velocity) override;
+    void clear_all() override;
+};