feat(settings): 站点界面动画总开关与子开关

管理后台可关全站动画，并细调代码折叠、平滑滚动、装饰入场；统一 lib/motion，尊重系统减少动态效果。

Co-authored-by: Cursor <cursoragent@cursor.com>

frontend/components/PostToc.tsx

@@ -1,6 +1,7 @@
 "use client";
 
 import { useEffect, useRef, useState } from "react";
+import { scrollBehavior } from "@/lib/motion";
 
 export interface TocItem {
   level: 2 | 3;
@@ -44,13 +45,12 @@ export default function PostToc({ items }: { items: TocItem[] }) {
     }
     const el = navRef.current?.querySelector<HTMLElement>(`[data-toc-id="${active}"]`);
     if (!el) return;
-    const reduce = window.matchMedia("(prefers-reduced-motion: reduce)").matches;
-    el.scrollIntoView({ block: "nearest", behavior: reduce ? "auto" : "smooth" });
+    el.scrollIntoView({ block: "nearest", behavior: scrollBehavior() });
   }, [active]);
 
   const jump = (id: string) => (e: React.MouseEvent) => {
     e.preventDefault();
-    document.getElementById(id)?.scrollIntoView({ behavior: "smooth", block: "start" });
+    document.getElementById(id)?.scrollIntoView({ behavior: scrollBehavior(), block: "start" });
   };
 
   return (