perf(mpc-system): 添加 Alpine 镜像加速配置

为所有 Dockerfile 的 builder 和 final 阶段添加阿里云镜像源：
- 使用 mirrors.aliyun.com 替代 dl-cdn.alpinelinux.org
- 显著加速中国区 Docker 构建中的 apk 包下载

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude <noreply@anthropic.com>

backend/mpc-system/services/account/Dockerfile

@@ -1,6 +1,9 @@
 # Build stage
 FROM golang:1.21-alpine AS builder
 
+# Use Aliyun mirror for Alpine packages (China acceleration)
+RUN sed -i 's/dl-cdn.alpinelinux.org/mirrors.aliyun.com/g' /etc/apk/repositories
+
 RUN apk add --no-cache git ca-certificates
 
 # Set Go proxy for China
@@ -23,6 +26,9 @@ RUN CGO_ENABLED=0 GOOS=linux GOARCH=amd64 go build \
 # Final stage
 FROM alpine:3.18
 
+# Use Aliyun mirror for Alpine packages (China acceleration)
+RUN sed -i 's/dl-cdn.alpinelinux.org/mirrors.aliyun.com/g' /etc/apk/repositories
+
 RUN apk --no-cache add ca-certificates curl
 RUN adduser -D -s /bin/sh mpc
 

backend/mpc-system/services/message-router/Dockerfile

@@ -1,6 +1,9 @@
 # Build stage
 FROM golang:1.21-alpine AS builder
 
+# Use Aliyun mirror for Alpine packages (China acceleration)
+RUN sed -i 's/dl-cdn.alpinelinux.org/mirrors.aliyun.com/g' /etc/apk/repositories
+
 RUN apk add --no-cache git ca-certificates
 
 # Set Go proxy for China
@@ -23,6 +26,9 @@ RUN CGO_ENABLED=0 GOOS=linux GOARCH=amd64 go build \
 # Final stage
 FROM alpine:3.18
 
+# Use Aliyun mirror for Alpine packages (China acceleration)
+RUN sed -i 's/dl-cdn.alpinelinux.org/mirrors.aliyun.com/g' /etc/apk/repositories
+
 RUN apk --no-cache add ca-certificates curl
 RUN adduser -D -s /bin/sh mpc
 

backend/mpc-system/services/server-party/Dockerfile

@@ -1,6 +1,9 @@
 # Build stage
 FROM golang:1.21-alpine AS builder
 
+# Use Aliyun mirror for Alpine packages (China acceleration)
+RUN sed -i 's/dl-cdn.alpinelinux.org/mirrors.aliyun.com/g' /etc/apk/repositories
+
 RUN apk add --no-cache git ca-certificates
 
 # Set Go proxy for China
@@ -23,6 +26,9 @@ RUN CGO_ENABLED=0 GOOS=linux GOARCH=amd64 go build \
 # Final stage
 FROM alpine:3.18
 
+# Use Aliyun mirror for Alpine packages (China acceleration)
+RUN sed -i 's/dl-cdn.alpinelinux.org/mirrors.aliyun.com/g' /etc/apk/repositories
+
 RUN apk --no-cache add ca-certificates curl
 RUN adduser -D -s /bin/sh mpc
 

backend/mpc-system/services/session-coordinator/Dockerfile

@@ -1,6 +1,9 @@
 # Build stage
 FROM golang:1.21-alpine AS builder
 
+# Use Aliyun mirror for Alpine packages (China acceleration)
+RUN sed -i 's/dl-cdn.alpinelinux.org/mirrors.aliyun.com/g' /etc/apk/repositories
+
 # Install dependencies
 RUN apk add --no-cache git ca-certificates
 
@@ -30,6 +33,9 @@ RUN CGO_ENABLED=0 GOOS=linux GOARCH=amd64 go build \
 # Final stage
 FROM alpine:3.18
 
+# Use Aliyun mirror for Alpine packages (China acceleration)
+RUN sed -i 's/dl-cdn.alpinelinux.org/mirrors.aliyun.com/g' /etc/apk/repositories
+
 # Install ca-certificates and curl for HTTPS and health check
 RUN apk --no-cache add ca-certificates curl