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.cpp

@@ -0,0 +1,41 @@
+// components/hal/switch_stub.cpp
+#include "hal/switch_stub.h"
+#include "esp_log.h"
+
+static const char* TAG = "switch_stub";
+
+DefaultSwitchStub::DefaultSwitchStub() : initialized(false) {
+    for (int i = 0; i < NUM_SWITCHES; i++) {
+        switch_states[i].id = i;
+        switch_states[i].gpio_pin = 0;
+        switch_states[i].current_state = false;
+        switch_states[i].previous_state = false;
+        switch_states[i].last_change_time = 0;
+        switch_states[i].debounce_time = 50;
+    }
+}
+
+void DefaultSwitchStub::begin() {
+    initialized = true;
+    ESP_LOGI(TAG, "Switch stub initialized (GPIO pins not configured yet)");
+}
+
+bool DefaultSwitchStub::is_pressed(uint8_t switch_id) {
+    if (!initialized || switch_id >= NUM_SWITCHES) {
+        return false;
+    }
+    return switch_states[switch_id].current_state;
+}
+
+void DefaultSwitchStub::configure_switch(uint8_t switch_id, uint8_t gpio_pin) {
+    if (switch_id >= NUM_SWITCHES) return;
+    switch_states[switch_id].gpio_pin = gpio_pin;
+    ESP_LOGI(TAG, "Switch %d configured to GPIO %d", switch_id, gpio_pin);
+}
+
+void DefaultSwitchStub::set_debounce_time(uint32_t time_ms) {
+    for (int i = 0; i < NUM_SWITCHES; i++) {
+        switch_states[i].debounce_time = time_ms;
+    }
+    ESP_LOGI(TAG, "Debounce time set to %lu ms", time_ms);
+}