docs(engineering): I8/I9 iteration artifacts and frontend UI specification

Add I8/I9 design and implementation review markdown, update parallel iteration
index and I7 review cross-links, and add FRONTEND_UI_SPECIFICATION for design
handoff (Figma Make).

Made-with: Cursor

docs/engineering/iterations/I9_IMPLEMENTATION_REVIEW.md

@@ -0,0 +1,44 @@
+# I9 实现审核 — 对照 [I9_WEBHOOK_DELIVERY_VISIBILITY_DESIGN.md](./I9_WEBHOOK_DELIVERY_VISIBILITY_DESIGN.md)
+
+> **日期**：2026-04-07。
+
+---
+
+## 1. 总评
+
+
+| 设计条款                        | 结论                                                                                                                               |
+| --------------------------- | -------------------------------------------------------------------------------------------------------------------------------- |
+| Webhook 只读 `GET by-receipt` | **已落地**：`PlatformDeliveryService#getStatusByReceiptId` + `WebhookPlatformDeliveryOpsController`。                                 |
+| 平台代理 + JWT                  | **已落地**：`GET /api/v1/callback-inbox/{id}/webhook-delivery`，`WebhookDeliveryReplayClient#fetchDeliveryStatus`。                    |
+| 前端不直连 Webhook               | **已落地**：`getCallbackWebhookDelivery` + 详情 `el-descriptions`；失败仅提示文案不遮断主详情。                                                       |
+| OpenAPI                     | **已导出**：`UPDATE_OPENAPI=1` 更新 `contracts/openapi/delivery-platform-api.json`。                                                    |
+| 文档索引 / I7 复盘                | **已修订**：[PARALLEL_ITERATION_INDEX](../PARALLEL_ITERATION_INDEX.md)、[I7_IMPLEMENTATION_REVIEW](./I7_IMPLEMENTATION_REVIEW.md) §2。 |
+
+
+---
+
+## 2. 后续（未在本迭代范围）
+
+
+| 项              | 说明                                              |
+| -------------- | ----------------------------------------------- |
+| **Playwright** | 可对「有 webhookReceiptId 的详情」断言状态区块或 503 提示。       |
+| **指标**         | M5-F08：积压 `PENDING`/`DEAD` 仍以观测平台为准，本迭代仅 UI 只读。 |
+
+
+---
+
+## 3. 验证
+
+- `JAVA_HOME`=JDK **17**：`mvn -f services/pom.xml verify`
+- `npm run build`（`web/delivery-platform-ui`）
+
+---
+
+## 4. 修订记录
+
+
+| 日期         | 说明  |
+| ---------- | --- |
+| 2026-04-07 | 初版。 |