feat(web+api): 贡献表单按 archive_kind 动态生成字段

- categories 接口返回 archive_kind
- 新增公开只读接口 /api/v1/kind-fields?kind=X 返回字段模板
- 投稿 payload 支持通用 attributes,审核通过写入 product.attributes (JSONB 合并)
- food_detail 仅在含食品数据时才 upsert (药品/3C/通用不再产生空行)
- 前端 Contribute 按所选品类 archive_kind 动态渲染字段
  (食品营养 / 药品 18 字段 / 3C / 通用),除商品名外均选填

Co-Authored-By: Devin AI <158243242+devin-ai-integration[bot]@users.noreply.github.com>

public-frontend/src/api.ts

@@ -1,4 +1,4 @@
-import type { Category, Product, ProductSummary, SubmissionInput } from "./types";
+import type { Category, KindField, Product, ProductSummary, SubmissionInput } from "./types";
 
 async function req<T>(path: string, init?: RequestInit): Promise<T> {
   const res = await fetch(path, {
@@ -67,6 +67,10 @@ export const api = {
   },
   product: (id: string) => req<Product>(`/api/v1/products/${id}`),
   categories: () => req<{ items: Category[] }>(`/api/v1/categories`),
+  kindFields: (kind: string) =>
+    req<{ items: KindField[]; kind: string }>(
+      `/api/v1/kind-fields?kind=${encodeURIComponent(kind)}`,
+    ),
   submit: (input: SubmissionInput) =>
     req<{ id: string; status: string }>(`/api/public/submissions`, {
       method: "POST",