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

scripts/Statemachine/EntityBase.gd

@@ -161,8 +161,8 @@ func _physics_process(_delta: float) -> void:
 
 # 通用方法
 func applyLevel():
-	fields[FieldStore.Entity.MAX_HEALTH] *= (1 + GameRule.entityHealthIncreasePerWave * (GameRule.difficulty + 1)) ** level
-	fields[FieldStore.Entity.DAMAGE_MULTIPILER] *= (1 + GameRule.entityDamageIncreasePerWave * (GameRule.difficulty + 1)) ** level
+	fields[FieldStore.Entity.MAX_HEALTH] *= (1 + GameRule.entityHealthIncreasePerWave * sqrt(GameRule.difficulty + 1)) ** level
+	fields[FieldStore.Entity.DAMAGE_MULTIPILER] *= (1 + GameRule.entityDamageIncreasePerWave * sqrt(GameRule.difficulty + 1)) ** level
 func displace(direction: Vector2, isSprinting: bool = false):
 	return (direction if isSprinting else direction.normalized()) * fields.get(FieldStore.Entity.MOVEMENT_SPEED) * 400 * abs(animatree.get("parameters/blend_position"))
 func move(direction: Vector2, isSprinting: bool = false):
@@ -255,7 +255,7 @@ func tryDie(by: BulletBase):
 		var item = drops[drop]
 		var count = ceil(randf_range(dropCounts[drop].x, dropCounts[drop].y))
 		for i in range(count):
-			ItemDropped.generate(item, count, position + MathTool.randv2_range(GameRule.itemDroppedSpawnOffset))
+			ItemDropped.generate(item, 1, position + MathTool.randv2_range(GameRule.itemDroppedSpawnOffset))
 	if MathTool.rate(
 		GameRule.appleDropRate +
 		by.launcher.fields.get(FieldStore.Entity.DROP_APPLE_RATE) +

scripts/Statemachine/SkillIcon.gd

@@ -4,6 +4,10 @@ class_name SkillIcon
 @export var weapon: Weapon = null;
 
 @onready var textureRect: TextureRect = $"%texture"
+@onready var particle: GPUParticles2D = $"%particle"
+
+var showed: bool = false
+
 func _ready():
 	material = material.duplicate()
 func _physics_process(_delta):
@@ -11,3 +15,9 @@ func _physics_process(_delta):
 		textureRect.texture = weapon.avatarTexture
 		var progress = min(weapon.cooldownTimer.timeSinceLastStart() / weapon.cooldownTimer.cooldown, UIState.player.energy / weapon.needEnergy)
 		material.set_shader_parameter("progress", progress)
+		if progress >= 1:
+			if !showed:
+				showed = true
+				particle.emitting = true
+		else:
+			showed = false

scripts/Tools/GameRule.gd

@@ -9,7 +9,7 @@ enum Difficulty {
 	MASTER,
 }
 static var deadReasons: Array = JsonTool.parseJson("res://resources/constants/deadReasons.json")
-static var difficulty: Difficulty = Difficulty.NORMAL # 难度倍数，可以写小数
+static var difficulty: Difficulty = Difficulty.MASTER # 难度倍数，可以写小数
 static var allowFriendlyFire: bool = false # 是否允许友军伤害
 static var bulletSpeedMultiplier: float = 1 # 子弹速度倍率
 static var damageOffset: float = MathTool.percent(20) # 伤害随机浮动比例