fix(frontend): 修复合并审阅发现的构建与契约问题

恢复 Vue TypeScript 生产构建，补齐可运行页面壳子，并修复文件树与 SSE 状态问题。

按 FastAPI Wire Contract 统一 Service DTO 映射，同时补充前端开发说明和问题修复复盘。

frontend/src/services/apiClient.ts

@@ -1,6 +1,11 @@
 import type { ApiError, ErrorResponse } from '@/contracts'
 
-const BASE_URL = import.meta.env.VITE_API_BASE || ''
+const BASE_URL = import.meta.env.VITE_API_BASE_URL ?? import.meta.env.VITE_API_BASE ?? ''
+
+export function resolveApiUrl(path: string): string {
+  if (/^https?:\/\//i.test(path)) return path
+  return `${BASE_URL.replace(/\/$/, '')}/${path.replace(/^\//, '')}`
+}
 
 interface RequestOptions extends RequestInit {
   params?: Record<string, string | number | boolean | undefined>
@@ -22,7 +27,7 @@ export class ApiErrorClass extends Error {
 async function request<T>(path: string, options: RequestOptions = {}): Promise<T> {
   const { params, token, headers, ...rest } = options
 
-  let url = path.startsWith('http') ? path : `${BASE_URL}${path}`
+  let url = resolveApiUrl(path)
 
   if (params) {
     const usp = new URLSearchParams()
@@ -94,6 +99,13 @@ export const apiClient = {
       body: body !== undefined ? JSON.stringify(body) : undefined,
     })
   },
+  put<T>(path: string, body?: unknown, options?: Omit<RequestOptions, 'method' | 'body'>) {
+    return request<T>(path, {
+      ...options,
+      method: 'PUT',
+      body: body !== undefined ? JSON.stringify(body) : undefined,
+    })
+  },
   delete<T>(path: string, options?: Omit<RequestOptions, 'method'>) {
     return request<T>(path, { ...options, method: 'DELETE' })
   },