- New ROS2 node: power_supervisor_node for battery state monitoring
- Battery thresholds: 30% warning, 20% dock search, 10% graceful shutdown, 5% force kill
- Charge cycle tracking and battery health estimation
- CSV logging to battery_log.csv for external analysis
- Publishes /saltybot/power_state for MQTT relay
- Graceful shutdown cascade: save state, stop motors, disarm on critical low battery
- Replaces/extends Issue #125 battery_node with supervisor-level power management
Co-Authored-By: Claude Haiku 4.5 <noreply@anthropic.com>
