feat: 添加掉落物功能，更新饲料和物品显示，重构相关UI组件

project.godot

@@ -21,6 +21,7 @@ project/assembly_name="ChickenVSBear"
 
 [gui]
 
+theme/custom="res://themes/main.tres"
 theme/custom_font="res://resources/fonts/HarmonyOS_Sans_Regular.ttf"
 
 [input]
@@ -56,6 +57,11 @@ sprint={
 ]
 }
 
+[physics]
+
+2d/default_gravity=0.0
+2d/default_linear_damp=1.0
+
 [rendering]
 
 renderer/rendering_method="gl_compatibility"