fix(tui): 修复 OpenTUI renderer 启动 crash

- externalOutputMode 'capture-stdout' 需要 screenMode 'split-footer'
  → 改为 'passthrough' + 'alternate-screen' 组合
- TUI 正常启动验证: header/tasks panel/footer/input/stats 全渲染

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

packages/tui/src/TuiApp.tsx

@@ -124,7 +124,7 @@ export class TuiApp {
       autoFocus: false,
       exitOnCtrlC: false,
       screenMode: 'alternate-screen',
-      externalOutputMode: 'capture-stdout',
+      externalOutputMode: 'passthrough',
       consoleMode: 'disabled',
       clearOnShutdown: true,
       openConsoleOnError: false,