feat(UI): 优化技能图标视觉效果并调整UI布局

- 为技能图标添加粒子效果，在冷却完成时显示
- 调整冷却进度条的着色器参数，改进视觉效果
- 修改默认游戏难度为MASTER
- 重构UI布局，将技能图标整合到能量条容器中
- 调整实体升级公式，使用平方根计算难度加成

shaders/CooldownProgress.gdshader

@@ -1,19 +1,19 @@
 shader_type canvas_item;
 uniform float progress:hint_range(-0.0, 2.0, 0.01)=0.5;
-uniform float backAlpha:hint_range(0.0, 1.0, 0.01)=0.25;
+uniform float backAlpha:hint_range(0.0, 1.0, 0.01)=0.1;
 uniform float edgeHeight:hint_range(0.0, 1.0, 0.01)=0.05;
+uniform vec4 edgeColor:source_color;
 uniform float trailHeight:hint_range(0.0, 1.0, 0.01)=0.3;
-uniform float trailAlpha:hint_range(0.0, 1.0, 0.01)=0.5;
+uniform vec4 trailColor:source_color;
 void fragment() {
 	if(UV.y>=1.0-progress){
 		if(1.0-progress+trailHeight-UV.y>0.0){
 			float dist=distance(UV.y,1.0-progress);
-			COLOR=vec4(1);
-			COLOR.a=(trailHeight-dist)/trailHeight*trailAlpha;
+			COLOR=mix(COLOR,trailColor*vec4(1,1,1,(trailHeight-dist)/trailHeight),1);
 		}else{
 			COLOR.a*=backAlpha;
 		}
 	}else if(distance(UV.y,1.0-progress)<edgeHeight){
-		COLOR=vec4(1.0);
+		COLOR=edgeColor;
 	}
 }