Adds saltybot_bringup.launch.py with ordered startup groups (drivers→
perception→navigation→UI), timer-based health gates, configurable
profiles (minimal/full/debug), and estop on Ctrl-C shutdown.
Also adds launch_profiles.py dataclass module and 53-test coverage for
profile hierarchy, timing gates, safety bounds, and to_dict serialization.
Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>
