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/hid/hid_device.hpp

@@ -0,0 +1,16 @@
+#pragma once
+
+// ==============================================================================
+// Virtual HID gamepad presentation
+// ==============================================================================
+// Exposes connected controllers to macOS so games recognize them natively.
+// Preferred path: DriverKit extension implementing IOHIDDriver with an
+// Xbox 360/One-compatible report descriptor (input reports from GIP, output
+// reports for rumble relayed back via GIP).
+// ==============================================================================
+
+namespace xone::hid {
+
+// TODO(phase 4): report descriptor + virtual device presentation.
+
+} // namespace xone::hid