chore: seal Design Vision v1 and monorepo scaffold

Archive the differentiated YuXinGu product docs, AI engineering system,
design contract, and Go/Vue scaffold. Next execution prioritizes Cece-parity
over early innovation (see .ai/product/STRATEGY.md).

Co-authored-by: Cursor <cursoragent@cursor.com>

packages/sdk/src/index.ts

@@ -0,0 +1,75 @@
+import type { ApiResponse } from '@yuxingu/types'
+
+/** Platform adapters so H5 and mini-program share one client. */
+export interface RequestOptions {
+  method?: 'GET' | 'POST' | 'PUT' | 'DELETE'
+  path: string
+  body?: unknown
+  headers?: Record<string, string>
+}
+
+export interface ClientAdapters {
+  /** Perform HTTP and return parsed JSON envelope. */
+  request: <T>(opts: RequestOptions) => Promise<ApiResponse<T>>
+  getToken?: () => string | null | Promise<string | null>
+}
+
+export interface CreateClientOptions {
+  baseURL: string
+  adapters: ClientAdapters
+}
+
+/**
+ * createClient builds a typed API facade.
+ * Side effect: network via adapters.request.
+ */
+export function createClient(opts: CreateClientOptions) {
+  const { baseURL, adapters } = opts
+
+  async function call<T>(path: string, init?: Omit<RequestOptions, 'path'>): Promise<T> {
+    const token = adapters.getToken ? await adapters.getToken() : null
+    const headers: Record<string, string> = { ...(init?.headers || {}) }
+    if (token) headers.Authorization = `Bearer ${token}`
+
+    const res = await adapters.request<T>({
+      method: init?.method || 'GET',
+      path: joinURL(baseURL, path),
+      body: init?.body,
+      headers,
+    })
+    if (res.code !== 0) {
+      throw new Error(res.message || `api error ${res.code}`)
+    }
+    return res.data as T
+  }
+
+  return {
+    healthz: () => call<{ status: string }>('/api/v1/healthz'),
+    ping: () => call<{ pong: boolean }>('/api/v1/ping'),
+  }
+}
+
+/** Browser fetch adapter for user-h5. */
+export function createBrowserAdapters(): ClientAdapters {
+  return {
+    request: async <T>({ method = 'GET', path, body, headers }) => {
+      const res = await fetch(path, {
+        method,
+        headers: {
+          'Content-Type': 'application/json',
+          ...(headers || {}),
+        },
+        body: body === undefined ? undefined : JSON.stringify(body),
+      })
+      return (await res.json()) as ApiResponse<T>
+    },
+    getToken: () => localStorage.getItem('yxg_token'),
+  }
+}
+
+function joinURL(base: string, path: string): string {
+  if (path.startsWith('http')) return path
+  const b = base.replace(/\/$/, '')
+  const p = path.startsWith('/') ? path : `/${path}`
+  return `${b}${p}`
+}