chore(gen1): 第一代版本封板 — DSH 2.0.17 兼容 + settings API 迁移 + React #130 修复

- peerDeps 升级到 0.2.0-rc.2
- settings API 迁移: register() → describe() + settings/document-updated
- turnTail slots.register 补 id 字段
- EditorHost viewer.component undefined guard
- 56/56 测试全绿, typecheck/build 通过

tag: v1.2.0-gen1

src/client/EditorHost.tsx

@@ -483,7 +483,7 @@ export function EditorHost(props: {
             ? <FenceErrorNotice store={store} onDisabled={() => { setReloadSeq(sequence => sequence + 1) }} />
             : <div className={css.editorError}>{load.message}</div>)}
           {!showEmpty && load.status === 'binary' && <BinaryDownload scope={scope} path={path} />}
-          {!showEmpty && load.status === 'ready' && createElement(load.viewer.component, {
+          {!showEmpty && load.status === 'ready' && load.viewer.component !== undefined && createElement(load.viewer.component, {
             ctx, store, scope, path, title,
             viewerId: load.viewer.id,
             content: load.content,