fix(modal): compensate scrollbar width when locking page scroll

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

assets/js/core/modal-runtime.js

@@ -38,9 +38,43 @@
       .replace(/'/g, "'");
   }
 
+  // 参考主题 Bootstrap Modal setScrollbar/resetScrollbar 等价物：
+  // overflow:hidden 会去掉页面滚动条，版心与 fixed 顶栏随之变宽而横向跳动，
+  // 因此锁定前测量滚动条宽度，给 body 与 fixed 元素补同宽 padding-right，解锁时还原。
+  var SCROLLBAR_FIXED = ".nav-fixed .header, .float-right";
+  var scrollLock = null;
+
+  function padRight(element, gap) {
+    var inline = element.style.paddingRight;
+    var computed = parseFloat(window.getComputedStyle(element).paddingRight) || 0;
+    element.style.paddingRight = computed + gap + "px";
+    return { element: element, inline: inline };
+  }
+
   function lockScroll(lock) {
-    document.documentElement.classList.toggle("aksrt-modal-runtime-open", !!lock);
-    document.body.classList.toggle("aksrt-modal-runtime-open", !!lock);
+    var html = document.documentElement;
+    var body = document.body;
+    if (lock) {
+      if (scrollLock) return;
+      var gap = window.innerWidth - html.clientWidth;
+      scrollLock = [];
+      if (gap > 0) {
+        scrollLock.push(padRight(body, gap));
+        document.querySelectorAll(SCROLLBAR_FIXED).forEach(function (element) {
+          scrollLock.push(padRight(element, gap));
+        });
+      }
+      html.classList.add("aksrt-modal-runtime-open");
+      body.classList.add("aksrt-modal-runtime-open");
+      return;
+    }
+    if (!scrollLock) return;
+    html.classList.remove("aksrt-modal-runtime-open");
+    body.classList.remove("aksrt-modal-runtime-open");
+    scrollLock.forEach(function (entry) {
+      entry.element.style.paddingRight = entry.inline;
+    });
+    scrollLock = null;
   }
 
   function skeleton(options) {