fix: Fix critical TUI issues

- Use password mode for API Key input (security)
- Fix input box display with proper CSS
- Fix message sending crash with safe handling
- Simplify message processing to avoid async issues
- Add error handling and user feedback
- Improve input field styling

graph_memory_tui/widgets/config_section.py

@@ -29,7 +29,7 @@ class ConfigSection(Vertical):
             value=self._config.api_key,
             placeholder="sk-xxxxxxxxxxxxx",
             id="api-key-input",
-            password=False
+            password=True  # 使用密码模式
         )
         yield Static("模型:", classes="config-label")
         yield Input(