tmux: add self-heal flow and harden wrapper verification

[dmoliveira]

Summary

• add make tmux-self-heal backed by scripts/tmux_self_heal.sh to install/update tmux plugins, validate formatter availability, and reload tmux config in one command
• switch pre-commit shfmt-local to check mode (-d) so CI/release checks fail cleanly without mutating scripts
• add a cross-platform smoke job in .github/workflows/smoke-checks.yml to validate run_commands/tmux_network_bandwidth_safe behavior on Linux and macOS

Validation

• make tmux-self-heal
• make verify
• pre-commit run --all-files
• make ci-quick