docker: use Chinese mirrors to speed up build

Dockerfile

@@ -1,10 +1,11 @@
 FROM golang:1.26-alpine AS build
 
-RUN apk add --no-cache git
+RUN sed -i 's/dl-cdn.alpinelinux.org/mirrors.aliyun.com/g' /etc/apk/repositories \
+    && apk add --no-cache git
 
 WORKDIR /src
 COPY go.mod go.sum ./
-RUN go mod download
+RUN go env -w GOPROXY=https://goproxy.cn,direct && go mod download
 
 COPY . .
 
@@ -18,7 +19,9 @@ RUN CGO_ENABLED=0 GOOS=linux go build \
 # ── Runtime ──
 FROM alpine:3.20
 
-RUN apk add --no-cache ca-certificates tzdata
+RUN sed -i 's/dl-cdn.alpinelinux.org/mirrors.aliyun.com/g' /etc/apk/repositories \
+    && apk add --no-cache ca-certificates tzdata \
+    && rm -rf /var/cache/apk/*
 
 WORKDIR /app
 COPY --from=build /out/monitor-server .
@@ -27,7 +30,6 @@ COPY server.yaml .
 RUN mkdir -p data
 
 EXPOSE 8080
-
 VOLUME ["/app/data"]
 
 ENTRYPOINT ["./monitor-server"]