WIP: checkpoint Wii native IMU and upstream IR bridge

Pause Wii pointing work with firmware 0.33-wii-trace installed. Preserve the pinned libogc IR pipeline, calibrated native IMU, software BOOTSEL, and standard camera sensitivity trial.

Tracking instability, tracking loss, and ineffective vertical movement remain unresolved. Level-2 camera filtering is not hardware-qualified. Nine targeted regression tests pass; firmware and persistent storage were verified after flashing.

tools/switch2_usb_probe/bootsel.cpp

@@ -0,0 +1,35 @@
+#include "bootsel.h"
+
+#include "adapter/adapter_mode_controller.h"
+#include "usb/usb_configuration_management.h"
+
+namespace {
+bool bootsel_accepted;
+}
+
+bool probe_bootsel_vendor_control(uint8_t rhport, uint8_t stage,
+                                  const tusb_control_request_t* request) {
+    using namespace UsbConfigurationManagement;
+    if (request == nullptr || request->bmRequestType != 0x40 ||
+        request->bRequest != static_cast<uint8_t>(Operation::kBootselReboot) ||
+        request->wValue != kRequestValue || request->wIndex != kRequestIndex ||
+        request->wLength != kRequestHeaderSize) {
+        return false;
+    }
+    // The shared handler receives the envelope at SETUP and validates and
+    // dispatches it only at ACK, after the host's control transfer completes.
+    const bool accepted =
+        usb_configuration_management_vendor_control(rhport, stage, request);
+    if (accepted && stage == CONTROL_STAGE_ACK) {
+        bootsel_accepted = true;
+    }
+    return accepted;
+}
+
+void probe_bootsel_task(uint32_t now_ms) {
+    // The native bridge does not initialize ordinary adapter-mode selection.
+    // A successful BOOTSEL dispatch guarantees the task takes its reboot path.
+    if (bootsel_accepted) {
+        adapter_mode_controller_task(now_ms);
+    }
+}