New saltybot_thermal package with thermal_node: reads all
/sys/class/thermal/thermal_zone* sysfs entries (millidegrees→°C),
publishes /saltybot/thermal JSON at 1 Hz with zones[], max_temp_c,
warn, and throttled flags. Logs ROS2 WARN at ≥75°C, ERROR at ≥85°C.
thermal_root param allows sysfs override for offline testing.
50/50 tests passing.
Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>
