ci: 切到 Gitea golang-1.25 runner, alpine 镜像

Gitea runner 现在用 golang-1.25 标签 (alpine + Go 1.25 预装), 不
再需要 wget + tar 装 Go. 删 "Install Go (Mirror in China)" step,
保留 GOPROXY 设置 (alpine 默认 GOPROXY=proxy.golang.org, 国内
runner 慢).

runner: golang-1.25 (两 job 都改)
step 1: actions/checkout@v4 (alpine 已有, 不需要 apt 装 git)
step 2: "Set GOPROXY" 写 \$GITHUB_ENV, 后续 step 继承
        (https://goproxy.cn/,https://goproxy.io,direct)

grep -P 兼容性 fix: alpine busybox grep 不支持 -P (PCRE). 之前
release job 用 grep -oP '"id":\s*\K[0-9]+' 拆 release id, 在
alpine 上会 "grep: unrecognized option". 改两次 grep -o:
  grep -o '"id":[0-9]*' | head -n 1 | grep -o '[0-9]*'
  第 1 个 grep 拉出 "id":<num>, 第 2 个去掉引号和 key 名.
不依赖 -P, POSIX grep 也跑.

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

.github/workflows/build.yml

@@ -2,9 +2,10 @@
 # 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.
+# Runner: golang-1.25 (Gitea-managed image, alpine + Go 1.25 preinstalled).
+# No Go installation step needed. GOPROXY is set explicitly to use the
+# China-region mirrors (default alpine GOPROXY is proxy.golang.org, which
+# is slow from this runner's network).
 name: CI / Release
 
 on:
@@ -18,19 +19,13 @@ on:
 jobs:
   ci:
     name: CI
-    runs-on: ubuntu-latest
+    runs-on: golang-1.25
     steps:
       - name: Checkout
         uses: actions/checkout@v4
 
-      - name: Install Go (Mirror in China)
+      - name: Set GOPROXY
         run: |
-          if [ ! -d "/usr/local/go" ]; then
-            wget https://mirrors.nju.edu.cn/golang/go1.25.5.linux-amd64.tar.gz
-            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/,https://goproxy.io,direct" >> $GITHUB_ENV
 
       - name: Build
@@ -66,19 +61,13 @@ jobs:
     name: Release
     needs: ci
     if: startsWith(github.ref, 'refs/tags/v')
-    runs-on: ubuntu-latest
+    runs-on: golang-1.25
     steps:
       - name: Checkout
         uses: actions/checkout@v4
 
-      - name: Install Go (Mirror in China)
+      - name: Set GOPROXY
         run: |
-          if [ ! -d "/usr/local/go" ]; then
-            wget https://mirrors.nju.edu.cn/golang/go1.25.5.linux-amd64.tar.gz
-            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/,https://goproxy.io,direct" >> $GITHUB_ENV
 
       - name: Build release binary
@@ -95,6 +84,7 @@ jobs:
 
           # 2. 调用 Gitea API 创建一个 Release 并获取其 ID
           # 注意：${{ github.api_url }} 会自动解析为你本地 Gitea 的 API 地址 (如 http://your-gitea/api/v1)
+          # alpine busybox grep 不支持 -P (PCRE), 改用两次 grep -o 拆 id
           RELEASE_ID=$(curl -X POST "${{ github.api_url }}/repos/${{ github.repository }}/releases" \
             -H "accept: application/json" \
             -H "authorization: token ${GITEA_TOKEN}" \
@@ -106,7 +96,7 @@ jobs:
               \"body\": \"Auto generated release assets.\",
               \"draft\": false,
               \"prerelease\": false
-            }" | grep -oP '"id":\s*\K[0-9]+' | head -n 1)
+            }" | grep -o '"id":[0-9]*' | head -n 1 | grep -o '[0-9]*')
 
           echo "Release 创建成功，ID 为: ${RELEASE_ID}"