docker: add server Dockerfile with multi-stage build

.dockerignore

@@ -0,0 +1,16 @@
+.git
+.gitignore
+.idea
+.vscode
+dist
+data
+client
+server
+*.exe
+*.test
+*.out
+*.zip
+Makefile
+package.bat
+LICENSE
+README.md

Dockerfile

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+FROM golang:1.26-alpine AS build
+
+RUN apk add --no-cache git
+
+WORKDIR /src
+COPY go.mod go.sum ./
+RUN go mod download
+
+COPY . .
+
+ARG VERSION=1.0.0
+ARG BUILD_TIME
+
+RUN CGO_ENABLED=0 GOOS=linux go build \
+    -ldflags "-s -w -X 'main.Version=${VERSION}' -X 'main.BuildTime=${BUILD_TIME}'" \
+    -o /out/monitor-server ./cmd/server
+
+# ── Runtime ──
+FROM alpine:3.20
+
+RUN apk add --no-cache ca-certificates tzdata
+
+WORKDIR /app
+COPY --from=build /out/monitor-server .
+COPY server.yaml .
+
+RUN mkdir -p data
+
+EXPOSE 8080
+
+VOLUME ["/app/data"]
+
+ENTRYPOINT ["./monitor-server"]