Add Brief Reactions to Extreme Combat Stress

Add a brief physical reaction when the operator experiences prolonged and extreme combat stress during sustained firefights. The effect could last approximately 1.5 to 2 seconds and include muffled audio, quiet breathing, slight camera instability, and an animation such as the operator briefly touching their head or adjusting their posture. Player movement should remain fully responsive, and a subtle audio cue could warn the player before the reaction begins. It should only occur after sustained exposure to combat rather than being triggered randomly by individual explosions.