Changelog
- Add warden_server/external/libsodium as a git submodule pointing at the CMake wrapper repo (pulls libsodium source as its own nested submodule)
- Rewrite warden_server/cmake/sodium.cmake to add_subdirectory the wrapper instead of depending on a system install or the retired neighbour submodule
- Builds libsodium in-tree alongside warden_server on every platform; no apt/vcpkg setup required on dev machines