Add shellSafeCommandRules() validation to install_command, build_command,
and start_command fields in both the Livewire UI and REST API layers.
These fields previously accepted arbitrary strings without validation,
unlike other shell-adjacent fields which already used this pattern.
Also adds comprehensive tests for rejection of dangerous input and
acceptance of legitimate build commands.
Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>
c9922c30c2