fix: 添加国内 Go 代理，移除自动安装插件，解决网络下载失败

backend/gateway/Dockerfile

@@ -2,6 +2,8 @@ FROM golang:1.26.1-alpine3.23 AS builder
 
 WORKDIR /app
 
+ENV GOPROXY=https://goproxy.cn,direct
+
 COPY go.mod ./
 COPY main.go ./
 

backend/services/user-svc/Dockerfile

@@ -2,14 +2,12 @@ FROM golang:1.26.1-alpine3.23 AS builder
 
 WORKDIR /app
 
+ENV GOPROXY=https://goproxy.cn,direct
+
 COPY go.mod ./
 COPY main.go ./
-COPY user.proto ./
 
 RUN go mod download
-RUN go install google.golang.org/protobuf/cmd/protoc-gen-go@latest
-RUN go install google.golang.org/grpc/cmd/protoc-gen-go-grpc@latest
-RUN protoc --go_out=. --go-grpc_out=. user.proto
 RUN go build -o user-svc main.go
 
 FROM alpine:3.23