fix: 修复聊天消息显示问题

- AuthScene: 修复节点路径错误 (WhaleFrame, UsernameInput)
- ChatManager: 修复 timestamp 类型转换 (String -> float)
- ChatMessage: 修复节点引用获取方式和 UI 显示
- ChatUI: 优化消息列表布局对齐

scenes/prefabs/ui/ChatMessage.tscn

@@ -4,8 +4,8 @@
 
 [node name="ChatMessage" type="Panel"]
 offset_right = 400.0
-offset_bottom = 100.0
 size_flags_horizontal = 3
+size_flags_vertical = 6
 script = ExtResource("1")
 
 [node name="VBoxContainer" type="VBoxContainer" parent="."]
@@ -18,28 +18,23 @@ grow_vertical = 2
 theme_override_constants/separation = 4
 
 [node name="UserInfoContainer" type="HBoxContainer" parent="VBoxContainer"]
-unique_name_in_owner = true
 layout_mode = 2
 theme_override_constants/separation = 8
 
 [node name="UsernameLabel" type="Label" parent="VBoxContainer/UserInfoContainer"]
-unique_name_in_owner = true
 layout_mode = 2
 theme_override_colors/font_color = Color(0.2, 0.4, 0.8, 1)
 theme_override_font_sizes/font_size = 14
 text = "Username"
 
 [node name="TimestampLabel" type="Label" parent="VBoxContainer/UserInfoContainer"]
-unique_name_in_owner = true
 layout_mode = 2
 theme_override_colors/font_color = Color(0.5, 0.5, 0.5, 1)
 theme_override_font_sizes/font_size = 12
 text = "12:34"
 
 [node name="ContentLabel" type="RichTextLabel" parent="VBoxContainer"]
-unique_name_in_owner = true
 layout_mode = 2
 size_flags_vertical = 3
 bbcode_enabled = true
-text = "Message content here"
 fit_content = true