fix(tui): 修复消息分类、侧栏切换、动画失效、TextArea导入

- _write_raw: 空字符串'' in msg永远为True导致所有消息归类为tool-ok，
  替换为正确的emoji标记(✅/❌/🤖)
- action_toggle_sidebar: Textual无.visible属性，改用has_class/addClass
- CSS .hidden: display:none阻止transition动画，改用width+opacity方案
- constants.py: 添加TextArea、Rule到Textual可用性检查导入列表

xcli_core/constants.py

@@ -102,7 +102,7 @@ except ImportError:
 try:
     from textual.app import App, ComposeResult
     from textual.containers import Container, Horizontal, Vertical, VerticalScroll
-    from textual.widgets import Header, Footer, Input, RichLog, Static, Button, Tree
+    from textual.widgets import Header, Footer, Input, RichLog, Static, Button, Tree, TextArea, Rule
     from textual.widgets.tree import TreeNode
     from textual.binding import Binding
     from textual.events import Mount