Rename fabro-proctitle to fabro-proc and add safe wrappers for all
process management primitives (signals, pre-exec hooks). This contains
all unsafe proc code behind a safe API so downstream crates no longer
need #[allow(unsafe_code)] or direct libc dependencies.
New modules: signal (process_alive, sigterm, sigkill, sigterm_process_group),
pre_exec (pre_exec_setsid, pre_exec_setpgid, pre_exec_pdeathsig),
title (existing proctitle code). Eliminates three duplicate process_alive
definitions and removes libc as a direct dep of fabro-cli and fabro-sandbox.
Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>
