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

tests/test_version.cpp

@@ -0,0 +1,22 @@
+#include "unity.h"
+
+#include "app/xone_api.h"
+
+#ifndef XONE_VERSION
+#define XONE_VERSION "0.1.0"
+#endif
+
+void setUp() {}
+void tearDown() {}
+
+void test_version_matches_project(void)
+{
+    TEST_ASSERT_EQUAL_STRING(XONE_VERSION, xone_version());
+}
+
+int main(void)
+{
+    UNITY_BEGIN();
+    RUN_TEST(test_version_matches_project);
+    return UNITY_END();
+}