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

CMakeLists.txt

@@ -0,0 +1,7 @@
+# Top-level CMake file for ESP-IDF project
+cmake_minimum_required(VERSION 3.16)
+
+set(EXTRA_COMPONENT_DIRS "components")
+
+include($ENV{IDF_PATH}/tools/cmake/project.cmake)
+project(loopy_midi_controller)