perf: Docker build 提速 — 去 gcc/musl-dev + CGO_ENABLED=0 + cache mount

- 移除 gcc musl-dev (纯 Go SQLite 不需要 CGO)
- CGO_ENABLED=1 → 0 (编译提速 ~2-3x)
- go mod download/go build 加 --mount=type=cache 跨构建复用

Dockerfile.embed

@@ -38,18 +38,21 @@ ARG TARGETARCH
 
 WORKDIR /app
 
-# Alpine 镜像源探测（清华 403 时自动回退阿里云/官方）// Logan.Li
+# 安装构建依赖（纯 Go SQLite 无需 gcc/musl-dev）// Logan.Li
 COPY scripts/setup-alpine-mirrors.sh /tmp/setup-alpine-mirrors.sh
 RUN chmod +x /tmp/setup-alpine-mirrors.sh && /tmp/setup-alpine-mirrors.sh && \
-    apk add --no-cache git ca-certificates tzdata gcc musl-dev
+    apk add --no-cache git ca-certificates tzdata
 
 ENV TZ=Asia/Shanghai
 ENV GOPROXY=https://goproxy.cn,direct
 ENV GONOSUMCHECK=*
+ENV GOMODCACHE=/go/pkg/mod
+ENV GOCACHE=/root/.cache/go-build
 
 # 复制后端 go.mod（利用 Docker 层缓存）
 COPY backend/go.mod backend/go.sum ./
-RUN go mod download
+RUN --mount=type=cache,target=/go/pkg/mod \
+    go mod download
 
 # 复制后端源码
 COPY backend/ ./
@@ -58,8 +61,10 @@ COPY backend/ ./
 RUN rm -rf static && mkdir -p static
 COPY --from=frontend-builder /app/dist/ static/
 
-# 构建后端二进制（跟随 TARGETARCH，Mac ARM 构建 linux/arm64 避免 CGO 交叉编译失败）// Logan.Li
-RUN CGO_ENABLED=1 GOOS=linux GOARCH=${TARGETARCH} go build \
+# 构建后端二进制（纯 Go 无 CGO，cache mount 增量编译）// Logan.Li
+RUN --mount=type=cache,target=/root/.cache/go-build \
+    --mount=type=cache,target=/go/pkg/mod \
+    CGO_ENABLED=0 GOOS=linux GOARCH=${TARGETARCH} go build \
     -ldflags="-w -s -X main.Version=${VERSION} -X main.BuildTime=${BUILD_TIME} -X main.GitCommit=${GIT_COMMIT}" \
     -o aiops .