chore: scaffold CMake build system

Add the CMake build for the Swift + C++ macOS port, mirroring the
refix layout: deps/ modules (Platform, Flags, Sanitizers, FindUnity),
per-module static libraries (usb, auth, mt76, gip, hid, api), a Swift
app entry point with a pure C bridge header, and a Unity test suite
behind BUILD_TESTING.

Swift requires the Ninja or Xcode generator; a guard in
CMakeLists.txt rejects anything else.

Co-Authored-By: qwen (qwen/qwen3.8-27b@q2_k_xl): scaffolded CMake build + tests

include/mt76/mt76.hpp

@@ -0,0 +1,20 @@
+#pragma once
+
+// ==============================================================================
+// MT76 chip protocol (MediaTek MT76xx radio in the dongle)
+// ==============================================================================
+// Port target: medusalix/xone transport/mt76.c + mt76.h + mt76_defs.h.
+// Firmware load (0x3800-byte chunks), EFUSE read, radio init (~80 register
+// writes), channel evaluation, beacon transmission, pairing mode, client
+// association and WCID/AES-CCMP key setup (encryption runs on-chip).
+// ==============================================================================
+
+#include <cstdint>
+
+namespace xone::mt76 {
+
+// Load the firmware image for the given dongle PID into the chip.
+// TODO(phase 3): port from xone_mt76_load_firmware().
+auto load_firmware(std::uint16_t pid, char const *firmware_path) -> bool;
+
+} // namespace xone::mt76