sprint-7: Commissioning wizard + relay ZN auto-tuner + NVS config + knob encoder

Python:
- autotuner.py: RelayAutoTuner (Astrom-Hagglund relay method) → TunerResult
  with Ku/Tu; TunerResult.to_pid_gains() applies ZN formulas
- commissioning_wizard.py: 4-phase state machine (RUDDER_LIMITS → SENSOR_CAL
  → AUTO_TUNE → DONE); transport-injected for testability; abort on invalid cal
- test_autotuner.py: 17 tests covering relay convergence, ZN formulas,
  wizard full-run, abort, ADC swap, identical-ADC guard

Firmware:
- nvs_config.h/cpp: NVS-backed CalibrationData store (adc limits, rudder angles,
  outer Kp/Ki/Kd, commissioned flag); float stored as uint32 via memcpy
- knob_encoder.h/cpp: quadrature rotary encoder on GPIO 16/17 with ISR Gray-code
  decode; knob_arm coil arms for 5 s window; updates heading setpoint ±1 deg/detent
- modbus_slave.cpp: COIL_CMD_KNOB_ARM now calls knob_encoder_set_armed()
- main.cpp: nvs_config_init/load at boot; apply commissioned calibration to
  rudder sensor and outer loop gains; start knob encoder task

Tests: 326 passed | Flash: 28.5%

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

firmware/ar_autopilot_v1/src/protocols/modbus_slave.cpp

@@ -33,6 +33,7 @@
 #include "../system/task_config.h"
 #include "modbus_registers.h"
 #include "nmea2000_consumer.h"
+#include "../hal/knob_encoder.h"
 #include "../safety/safety_monitor.h"
 
 namespace arautopilot::protocols::modbus {
@@ -461,6 +462,7 @@ Modbus::Error write_coil(uint16_t addr, bool value) {
             return Modbus::Error::SUCCESS;
         case COIL_CMD_KNOB_ARM:
             g_coils.knob_arm = value;
+            hal::knob_encoder_set_armed(value);
             return Modbus::Error::SUCCESS;
         default:
             return Modbus::Error::ILLEGAL_DATA_ADDRESS;