Manifest evaluation now tolerates unresolvable working directories on CI

Commands that compile and run Tuist manifests (including tuist graph, generate, dump, and plugin/package loading) previously failed when the process working directory could not be resolved by getcwd, which often happens on CI when earlier steps delete or replace the directory. The manifest loader now passes an explicit working directory and falls back to the shell-provided PWD when getcwd is unavailable, restoring execution without changing normal behavior.