vpn: add CMake snippet for VPN subsystem integration

app/vpn/CMakeLists_vpn.cmake

@@ -0,0 +1,64 @@
+# app/vpn/CMakeLists_vpn.cmake
+#
+# Include this file from the top-level moonlight-qt CMakeLists.txt:
+#
+#   include(app/vpn/CMakeLists_vpn.cmake)
+#
+# Prerequisites:
+#   Run scripts/build-boringtun.sh first to produce deps/boringtun/libboringtun.a
+
+# ─── boringtun static library ─────────────────────────────────────────────────
+
+set(BORINGTUN_LIB "${CMAKE_SOURCE_DIR}/deps/boringtun/libboringtun.a")
+
+if(NOT EXISTS "${BORINGTUN_LIB}")
+    message(FATAL_ERROR
+        "boringtun static library not found at ${BORINGTUN_LIB}\n"
+        "Run:  bash scripts/build-boringtun.sh --universal\n"
+        "then re-run CMake.")
+endif()
+
+add_library(boringtun STATIC IMPORTED)
+set_target_properties(boringtun PROPERTIES
+    IMPORTED_LOCATION "${BORINGTUN_LIB}"
+)
+
+# ─── VPN source files ──────────────────────────────────────────────────────────
+
+set(VPN_SOURCES
+    app/vpn/wireguardconfig.cpp
+    app/vpn/relayclient.cpp
+)
+
+if(APPLE)
+    list(APPEND VPN_SOURCES app/vpn/tunnelmanager_mac.mm)
+elseif(WIN32)
+    list(APPEND VPN_SOURCES app/vpn/tunnelmanager_win.cpp)   # future
+elseif(UNIX)
+    list(APPEND VPN_SOURCES app/vpn/tunnelmanager_linux.cpp) # future
+endif()
+
+# ─── Integration into moonlight-qt target ────────────────────────────────────
+# Replace moonlight-qt below with whatever your top-level CMakeLists calls the app target.
+
+target_sources(moonlight-qt PRIVATE ${VPN_SOURCES})
+
+target_include_directories(moonlight-qt PRIVATE
+    "${CMAKE_SOURCE_DIR}/app/vpn"
+)
+
+target_link_libraries(moonlight-qt PRIVATE boringtun)
+
+if(APPLE)
+    # Frameworks required by boringtun on macOS
+    target_link_libraries(moonlight-qt PRIVATE
+        "-framework Security"
+        "-framework Network"
+        "-framework SystemConfiguration"
+    )
+    # Objective-C++ needed for tunnelmanager_mac.mm
+    set_source_files_properties(
+        app/vpn/tunnelmanager_mac.mm
+        PROPERTIES COMPILE_FLAGS "-fobjc-arc"
+    )
+endif()