ci: 改 workflow 用国内镜像装 Go + goproxy.cn 加速

之前 ci/release 两个 job 用 actions/setup-go@v5 从 go.mod 装 Go,
内置 cache. 在 Gitea runner 所在网络区域 (ping 23ms 短, 推测
国内) 跑得动但慢.

改用用户提供的脚本手动装 Go 1.25.5 (NJU 镜像) + goproxy.cn 代理
+ GITHUB_PATH/GITHUB_ENV (Gitea runner 也兼容这俩 env var).
actions/setup-go 整个去掉, 因为手动装后 PATH 跟 GOPROXY 都设好,
go build 直接可跑.

GITBUB_PATH/GITHUB_ENV 是 GitHub Actions 的特殊 file path env var,
Gitea Actions 兼容 (api-compatible). 写到这两个文件等价于在
后续 step 设置 PATH 和 环境变量.

保留 go build / go vet / go test / gofmt -l . 四项 CI gate.
保留 release job 的 tag 触发 + softprops/action-gh-release@v2 上传.

Co-Authored-By: Claude <noreply@anthropic.com>

.github/workflows/build.yml

@@ -1,6 +1,10 @@
 # This workflow runs on Gitea Actions, which is API-compatible with GitHub Actions.
 # It performs CI on every push to main and every pull request, and automatically
 # builds and attaches a Linux amd64 release binary when a version tag (v*) is pushed.
+#
+# Go is installed manually from a Chinese mirror (NJU) instead of using
+# actions/setup-go, because the runner is in a region where the official Go
+# download endpoint is slow. GOPROXY is set to goproxy.cn for the same reason.
 name: CI / Release
 
 on:
@@ -19,11 +23,15 @@ jobs:
       - name: Checkout
         uses: actions/checkout@v4
 
-      - name: Set up Go
+      - name: Install Go (Mirror in China)
-        uses: actions/setup-go@v5
+        run: |
-        with:
+          if [ ! -d "/usr/local/go" ]; then
-          go-version-file: go.mod
+            wget https://mirrors.nju.edu.cn/golang/go1.25.5.linux-amd64.tar.gz
-          cache: true
+            sudo tar -C /usr/local -xzf go1.25.5.linux-amd64.tar.gz
+            rm go1.25.5.linux-amd64.tar.gz
+          fi
+          echo "/usr/local/go/bin" >> $GITHUB_PATH
+          echo "GOPROXY=https://goproxy.cn,direct" >> $GITHUB_ENV
 
       - name: Build
         run: go build ./...
@@ -50,11 +58,15 @@ jobs:
       - name: Checkout
         uses: actions/checkout@v4
 
-      - name: Set up Go
+      - name: Install Go (Mirror in China)
-        uses: actions/setup-go@v5
+        run: |
-        with:
+          if [ ! -d "/usr/local/go" ]; then
-          go-version-file: go.mod
+            wget https://mirrors.nju.edu.cn/golang/go1.25.5.linux-amd64.tar.gz
-          cache: true
+            sudo tar -C /usr/local -xzf go1.25.5.linux-amd64.tar.gz
+            rm go1.25.5.linux-amd64.tar.gz
+          fi
+          echo "/usr/local/go/bin" >> $GITHUB_PATH
+          echo "GOPROXY=https://goproxy.cn,direct" >> $GITHUB_ENV
 
       - name: Build release binary
         run: GOOS=linux GOARCH=amd64 go build -o spark-mcp-linux-amd64 ./main.go