feat: 增加通知板场景

- 增加通知板与用户交互，点击E，弹出通知消息
- 预留前端调用后端获取通知的接口，当不可用时，使用mock data

scenes/prefabs/items/notice_board.tscn

@@ -0,0 +1,19 @@
+[gd_scene load_steps=4 format=3 uid="uid://rdmrm7j4iokr"]
+
+[ext_resource type="Script" uid="uid://pnlgf420wktn" path="res://scenes/prefabs/items/NoticeBoard.gd" id="1_script"]
+[ext_resource type="Texture2D" uid="uid://b4aildrnhbpl4" path="res://assets/materials/NoticeBoard.png" id="2_sprite"]
+
+[sub_resource type="RectangleShape2D" id="RectangleShape2D_nb"]
+size = Vector2(160, 53.33333)
+
+[node name="NoticeBoard" type="StaticBody2D"]
+scale = Vector2(0.6, 0.6)
+script = ExtResource("1_script")
+
+[node name="Sprite2D" type="Sprite2D" parent="."]
+position = Vector2(0, -16)
+scale = Vector2(0.5, 0.5)
+texture = ExtResource("2_sprite")
+
+[node name="CollisionShape2D" type="CollisionShape2D" parent="."]
+shape = SubResource("RectangleShape2D_nb")