feat(核弹): 添加核弹警告背景并调整爆炸效果

为核弹添加半透明警告背景环，调整爆炸震动强度从500降至300
新增填充环和光照着色器，用于视觉效果
将核弹作为公鸡角色的默认武器

scripts/Contents/Bullets/NuclearBomb.gd

@@ -4,6 +4,7 @@ class_name NuclearBomb
 @onready var label: Label = $"%label"
 @onready var anchor: Node2D = $"%anchor"
 @onready var warn: ShaderStage = $"%warn"
+@onready var warnbg: ShaderStage = $"%warnbg"
 
 var countdown = 10000
 var radius = 500
@@ -11,6 +12,7 @@ var radius = 500
 func spawn():
 	hitbox.disabled = true
 	hitbox.shape.radius = radius
+	warnbg.size = Vector2.ONE * 2 * radius
 	anchor.global_rotation = 0
 func ai():
 	speed *= 0.99
@@ -23,5 +25,5 @@ func ai():
 func destroy(_b):
 	EffectController.create(ComponentManager.getEffect("NuclearExplosion"), global_position).shot()
 	hitbox.disabled = false
-	CameraManager.shake(5000, 500, func(_c, t, r): return t * r) # 震屏强度随进度递减
+	CameraManager.shake(5000, 300, func(_c, t, r): return t * r) # 震屏强度随进度递减
 	await TickTool.frame(5)