fix: 将编辑账单接口从 PATCH 改为 POST

- 修改后端路由：POST /api/bills/:id
- 修改前端 API 调用方法为 POST
- 移除临时添加的 CORS 中间件
- 解决生产环境 405 Method Not Allowed 问题

web/src/lib/api.ts

@@ -258,7 +258,7 @@ export interface UpdateBillResponse {
 
 export async function updateBill(id: string, patch: UpdateBillRequest): Promise<UpdateBillResponse> {
   const response = await apiFetch(`${API_BASE}/api/bills/${encodeURIComponent(id)}`, {
-    method: 'PATCH',
+    method: 'POST',
     headers: {
       'Content-Type': 'application/json',
     },