The use-pkg-config feature was added in the previous PR and conflicts
with SODIUM_LIB_DIR. The build script errors with:
"SODIUM_LIB_DIR is incompatible with SODIUM_USE_PKG_CONFIG.
Set the only one env variable"
Removed the explicit libsodium-sys-stable dependency since we're using
the SODIUM_LIB_DIR environment variable approach instead.
Co-Authored-By: Claude Sonnet 4.5 <noreply@anthropic.com>