feat(hooks): add setWidgetComponent for custom TUI components

- New ctx.ui.setWidgetComponent(key, factory) method
- Allows custom Component to render as widget without taking focus
- Unlike custom(), widget components render inline above editor
- Components are disposed when cleared or replaced
- Falls back to no-op in RPC/print modes

packages/coding-agent/test/compaction-hooks.test.ts

@@ -121,6 +121,7 @@ describe.skipIf(!API_KEY)("Compaction hooks", () => {
 				notify: () => {},
 				setStatus: () => {},
 				setWidget: () => {},
+				setWidgetComponent: () => {},
 				custom: async () => undefined as never,
 				setEditorText: () => {},
 				getEditorText: () => "",