fix: update backend/Dockerfile to Go 1.26.1 with multi-stage build

backend/Dockerfile

@@ -1,24 +1,80 @@
-FROM golang:1.25.7-alpine
+# =============================================================================
+# Sub2API Backend-Only Dockerfile
+# =============================================================================
+# Stage 1: Build Go backend
+# Stage 2: Final minimal runtime image
+# =============================================================================
 
-WORKDIR /app
+ARG GOLANG_IMAGE=golang:1.26.1-alpine
+ARG ALPINE_IMAGE=alpine:3.21
 
-# 安装必要的工具
-RUN apk add --no-cache git
+# -----------------------------------------------------------------------------
+# Stage 1: Backend Builder
+# -----------------------------------------------------------------------------
+FROM ${GOLANG_IMAGE} AS backend-builder
 
-# 复制go.mod和go.sum
-COPY go.mod go.sum ./
+ARG GOPROXY=https://goproxy.cn,direct
+ARG GOSUMDB=sum.golang.google.cn
+
+ENV GOPROXY=${GOPROXY}
+ENV GOSUMDB=${GOSUMDB}
 
-# 下载依赖
+# Install build dependencies
+RUN apk add --no-cache git ca-certificates tzdata
+
+WORKDIR /app
+
+# Copy go mod files first (better caching)
+COPY go.mod go.sum ./
 RUN go mod download
 
-# 复制源代码
+# Copy source code
 COPY . .
 
-# 构建应用
-RUN go build -o main ./cmd/server/
+# Build static binary
+RUN CGO_ENABLED=0 GOOS=linux go build \
+    -trimpath \
+    -ldflags="-s -w" \
+    -o /app/main \
+    ./cmd/server
+
+# -----------------------------------------------------------------------------
+# Stage 2: Final Runtime Image
+# -----------------------------------------------------------------------------
+FROM ${ALPINE_IMAGE}
+
+# Labels
+LABEL maintainer="Wei-Shaw <github.com/Wei-Shaw>"
+LABEL description="Sub2API - AI API Gateway Platform (backend-only)"
+LABEL org.opencontainers.image.source="https://github.com/Wei-Shaw/sub2api"
 
-# 暴露端口
+# Install runtime dependencies
+RUN apk add --no-cache \
+    ca-certificates \
+    tzdata \
+    && rm -rf /var/cache/apk/*
+
+# Create non-root user
+RUN addgroup -g 1000 sub2api && \
+    adduser -u 1000 -G sub2api -s /bin/sh -D sub2api
+
+# Set working directory
+WORKDIR /app
+
+# Copy binary with ownership
+COPY --from=backend-builder --chown=sub2api:sub2api /app/main /app/main
+
+# Create data directory
+RUN mkdir -p /app/data && chown sub2api:sub2api /app/data
+
+# Switch to non-root user
+USER sub2api
+
+# Expose port
 EXPOSE 8080
 
-# 运行应用
-CMD ["./main"]
+# Health check
+HEALTHCHECK --interval=30s --timeout=10s --start-period=10s --retries=3 \
+    CMD wget -q -T 5 -O /dev/null http://localhost:${SERVER_PORT:-8080}/health || exit 1
+
+CMD ["/app/main"]