refactor: 静态资源缓存破坏改为文件级哈希，重启不刷新未修改文件的缓存

- 启动时计算每个 JS/CSS 的 SHA-1 前 8 位作为版本号
- 文件不变则哈希不变，浏览器继续用缓存，重启零压力
- 替换全局 AssetVersion 为 assetV 模板函数，按文件路径查询哈希
- 移除 BuildPageData 中的全局版本号注入

templates/MetaLab-2026/html/posts/show.html

@@ -48,10 +48,10 @@
 {{/* MD 内容安全传递给 JS */}}
 <textarea id="postMdContent" style="display:none">{{.Post.Body}}</textarea>
 
-<link rel="stylesheet" href="/static/vditor/dist/index.css">
-<script src="/static/vditor/dist/method.min.js"></script>
-<script src="/static/js/common.js?v={{.V}}"></script>
-<script src="/static/js/shortcode.js?v={{.V}}"></script>
+<link rel="stylesheet" href="/static/vditor/dist/index.css?v={{assetV "/static/vditor/dist/index.css"}}">
+<script src="/static/vditor/dist/method.min.js?v={{assetV "/static/vditor/dist/method.min.js"}}"></script>
+<script src="/static/js/common.js?v={{assetV "/static/js/common.js"}}"></script>
+<script src="/static/js/shortcode.js?v={{assetV "/static/js/shortcode.js"}}"></script>
 <script>
 (function() {
     var el = document.getElementById('postContent');