fix: use DaoCloud mirror for base images to avoid Docker Hub timeout

backend/Dockerfile

@@ -1,4 +1,4 @@
-FROM python:3.12-slim
+FROM docker.m.daocloud.io/python:3.12-slim
 
 ENV PYTHONDONTWRITEBYTECODE=1
 ENV PYTHONUNBUFFERED=1

web/Dockerfile

@@ -1,5 +1,5 @@
 # ---- Build Stage ----
-FROM node:18-alpine AS builder
+FROM docker.m.daocloud.io/node:18-alpine AS builder
 
 RUN npm config set registry https://registry.npmmirror.com
 
@@ -10,7 +10,7 @@ COPY . .
 RUN npm run build
 
 # ---- Runtime Stage ----
-FROM nginx:alpine
+FROM docker.m.daocloud.io/nginx:alpine
 
 RUN sed -i 's#dl-cdn.alpinelinux.org#mirrors.aliyun.com#g' /etc/apk/repositories