Add coulomb counter for accurate SoC estimation independent of load:
- New coulomb_counter module: integrate current over time to track Ah consumed
* coulomb_counter_init(capacity_mah) initializes with battery capacity
* coulomb_counter_accumulate(current_ma) integrates current at 100 Hz
* coulomb_counter_get_soc_pct() returns SoC 0-100% (255 = invalid)
* coulomb_counter_reset() for charge-complete reset
- Battery module integration:
* battery_accumulate_coulombs() reads motor INA219 currents and accumulates
* battery_get_soc_coulomb() returns coulomb-based SoC with fallback to voltage
* Initialize coulomb counter at startup with DEFAULT_BATTERY_CAPACITY_MAH
- Telemetry updates:
* JLink STATUS: use coulomb SoC if available, fallback to voltage-based
* CRSF battery frame: now includes remaining capacity in mAh (from coulomb counter)
* CRSF capacity field was always 0; now reflects actual remaining mAh
- Mainloop integration:
* Call battery_accumulate_coulombs() every tick for continuous integration
* INA219 motor currents + 200 mA subsystem baseline = total battery draw
Motor current sources (INA219 addresses 0x40/0x41) provide most power draw;
Jetson ROS2 battery_node already prioritizes coulomb-based soc_pct from STATUS frame.
Default capacity: 2200 mAh (typical lab 3S LiPo); configurable via firmware parameter.
Co-Authored-By: Claude Haiku 4.5 <noreply@anthropic.com>
