Add player health, lives, death, and cutscene system

Added player damage, invulnerability frames, knockback, and death handling. Enemies stop attacking after player death and player controls are disabled. Added a persistent three-life system with ambulance cutscenes after the first two deaths and a final Game Over cutscene after the third death.

Scenes/Characters/Player.tscn

@@ -716,7 +716,7 @@ z_index = 10
 texture_filter = 1
 position = Vector2(0, -6)
 sprite_frames = SubResource("SpriteFrames_nn08x")
-animation = &"idle"
+animation = &"death"
 autoplay = "idle"
 
 [node name="ChildGraphic" type="AnimatedSprite2D" parent="."]