添加Docker部署配置：backend Dockerfile、Caddyfile、docker-compose.yml，支持腾云云服务器部署域名skin.khhao.com，使用Caddy反向代理 + HTTPS

Dockerfile.backend

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+FROM golang:1.26-alpine AS builder
+
+WORKDIR /app
+
+# Copy Go files
+COPY backend/go.mod backend/go.sum ./
+RUN go mod download
+
+COPY backend ./backend
+WORKDIR /app/backend
+
+# Build the Go binary
+RUN CGO_ENABLED=0 GOOS=linux go build -o /server ./cmd/server
+
+# Final stage
+FROM alpine:latest
+
+RUN apk --no-cache add ca-certificates tzdata
+
+WORKDIR /app
+
+COPY --from=builder /server ./server
+# Expose port
+EXPOSE 8080
+
+# Run the server
+CMD ["./server"]