Add laser temperature monitoring for current-variation runs

Independent monitor + checker for CHANGE_CURRENT_LD1 variation, where the
board sweeps LD1 current autonomously while both laser temperatures must stay
on their static setpoints. Nothing previously verified that the setpoints were
actually reached, so a stale temperature silently corrupted measurements.

New package python_app/hardware_full/laser_control/monitoring/:
- session.py: LaserVariationSession snapshot (targets + tolerance frozen at start)
- readings_channel.py: JSONL append/tail channel for per-sweep readings
- monitor.py: LaserTemperatureMonitor polls the board once per sweep, publishes
- checker.py: LaserTemperatureChecker validates temp1/temp2 vs targets (0.03 C),
  warns to console per laser with anti-spam state

CLI entry points scripts/laser_temp_monitor.py and scripts/laser_temp_checker.py
run as independent processes communicating via IPC files.

Also: add temp_tolerance_c to LaserVariationModeModel (schema + codec round-trip)
and write the session snapshot from apply_kamil_adc_laser_control's variation path
so the checker works with pipeline-started runs too.

Tests in tests/test_laser_temp_monitoring.py (17 cases); existing laser-control
protocol and config-codec suites remain green.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

python_app/scripts/laser_temp_monitor.py

@@ -26,6 +26,7 @@ from python_app.hardware_full.laser_control.controller import (
     DEVICE_MAIN_MESSAGE_ID,
     LaserController,
 )
+from python_app.hardware_full.laser_control.exceptions import PortBusyError
 from python_app.hardware_full.laser_control.models import VariationType
 from python_app.hardware_full.laser_control.monitoring import (
     DEFAULT_READINGS_PATH,
@@ -114,7 +115,13 @@ def main() -> int:
         pi_coeff2_p=laser.pi_coeff2_p,
         pi_coeff2_i=laser.pi_coeff2_i,
     )
+    try:
         controller.connect()
+    except PortBusyError as exc:
+        # Expected, benign conflict: the manual-control UI (or another monitor)
+        # already owns the port. Exit cleanly with guidance, not a traceback.
+        logger.error("%s", exc)
+        return 2
     try:
         if args.start:
             _start_variation(controller, variation)