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

shaders/FilledRing.gdshader

@@ -0,0 +1,13 @@
+shader_type canvas_item;
+uniform float inner:hint_range(0.0, 1.0, 0.01)=0.5;
+uniform float outer:hint_range(0.0, 1.0, 0.01)=0.75;
+uniform float alpha:hint_range(0.0, 1.0, 0.1)=0.5;
+void fragment() {
+	vec2 center=vec2(0.5);
+	float dist=distance(UV,center)*2.0;
+	if(dist<inner){
+		COLOR.a*=alpha;
+	}else{
+		COLOR.a*=float(inner<dist&&dist<outer);
+	}
+}

shaders/Light.gdshader

@@ -0,0 +1,9 @@
+shader_type canvas_item;
+uniform vec4 color:source_color;
+uniform float mixProgress:hint_range(0.0, 1.0, 0.01)=0.5;
+void fragment() {
+	float maxDistance=0.5;
+	float dist=distance(UV,vec2(0.5));
+	vec4 mixed=vec4(color.rgb,smoothstep(0,1,(maxDistance-dist)/maxDistance));
+	COLOR=mix(COLOR,mixed,mixProgress);
+}