feat(UI): 添加物品收集显示功能

- 新增CameraManager脚本用于相机管理
- 在UI场景中添加物品收集容器VBoxContainer
- 扩展ItemShow类支持生成物品显示实例
- 修改EntityBase添加物品收集信号和处理逻辑
- 调整BossBar位置和布局属性

components/UI/BossBar.tscn

@@ -27,9 +27,9 @@ anchor_left = 0.2
 anchor_top = 1.0
 anchor_right = 0.8
 anchor_bottom = 1.0
-offset_top = -40.0
+offset_top = -65.0
 offset_right = 0.0
-offset_bottom = -20.0
+offset_bottom = -40.0
 grow_horizontal = 2
 grow_vertical = 0
 
@@ -48,19 +48,16 @@ layout_mode = 2
 [node name="name" type="Label" parent="health/panel/label"]
 unique_name_in_owner = true
 layout_mode = 2
-size_flags_vertical = 8
 text = "BossName"
 label_settings = SubResource("LabelSettings_esyuk")
 
 [node name="value" type="Label" parent="health/panel/label"]
 unique_name_in_owner = true
 layout_mode = 2
-size_flags_vertical = 8
 text = "percent"
 label_settings = SubResource("LabelSettings_esyuk")
 
 [node name="percent" type="Label" parent="health/panel/label"]
 layout_mode = 2
-size_flags_vertical = 8
 text = "%"
 label_settings = SubResource("LabelSettings_esyuk")