Track and add motion_gating_comparison figure

Agent-Logs-Url: https://github.com/dfeen87/Smartphone-Based-Chest-Monitoring/sessions/13ce080f-7cc2-4c24-ab80-9d663adb7633

Co-authored-by: dfeen87 <158860247+dfeen87@users.noreply.github.com>

Author: Copilot

.gitignore

@@ -26,7 +26,8 @@ Thumbs.db
 *.tmp
 
 # Generated validation figures (produced at runtime by validate_bidmc.py)
-validation/figures/
+validation/figures/*
+!validation/figures/motion_gating_comparison.png
 
 # Python bytecode cache
 __pycache__/