feat(hooks): add setWidget API for multi-line status displays

- ctx.ui.setWidget(key, lines) for multi-line displays above editor
- Widgets appear below 'Working...' indicator, above editor
- Supports ANSI styling including strikethrough
- Added theme.strikethrough() method
- Plan-mode hook now shows todo list with checkboxes
- Completed items show checked box and strikethrough text

packages/coding-agent/src/core/hooks/runner.ts

@@ -49,6 +49,7 @@ const noOpUIContext: HookUIContext = {
 	input: async () => undefined,
 	notify: () => {},
 	setStatus: () => {},
+	setWidget: () => {},
 	custom: async () => undefined as never,
 	setEditorText: () => {},
 	getEditorText: () => "",