- Replace boost::program_options with header-only CLI11 in main.cpp
- Remove boost dependency from Makefile, default.nix, and flake.nix
- Update documentation in doc/BUILD.md
- Add CMakeLists.txt as an alternative build system
This fixes the issue where the binary would fail to find specific libboost_program_options.so versions (e.g., 1.90.0) on systems with newer/older Boost versions. Since CLI11 is header-only, there is no longer a runtime dependency on Boost for pcloudcc.