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/auth/crypto.hpp

@@ -0,0 +1,16 @@
+#pragma once
+
+// ==============================================================================
+// Auth + crypto
+// ==============================================================================
+// Port target: medusalix/xone auth/auth.c + auth/crypto.c.
+// ECDH (P-256) key agreement, RSA encryption, SHA transcript/PRF for the GIP
+// authentication handshake. AES-CCMP frame encryption itself runs on-chip;
+// this layer only derives and installs keys into the MT76 WCID registers.
+// ==============================================================================
+
+namespace xone::auth {
+
+// TODO(phase 1): ECDH/RSA/SHA primitives (CommonCrypto / Security.framework).
+
+} // namespace xone::auth