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/switch_stub.h

@@ -1,6 +1,8 @@
-// hal/switch_stub.h
+// components/hal/switch_stub.h
 #pragma once
 
+#include <cstdint>
+
 class SwitchStub {
 public:
     virtual ~SwitchStub() {}
@@ -21,4 +23,19 @@ struct SwitchState {
     bool previous_state;     // Previous state (for debounce)
     uint32_t last_change_time; // Timestamp of last state change
     uint32_t debounce_time;  // Debounce time in ms
-};
+};
+
+// Default stub implementation
+class DefaultSwitchStub : public SwitchStub {
+private:
+    static const uint8_t NUM_SWITCHES = 10;
+    SwitchState switch_states[NUM_SWITCHES];
+    bool initialized;
+    
+public:
+    DefaultSwitchStub();
+    void begin() override;
+    bool is_pressed(uint8_t switch_id) override;
+    void configure_switch(uint8_t switch_id, uint8_t gpio_pin) override;
+    void set_debounce_time(uint32_t time_ms) override;
+};