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/app/layout.tsx

@@ -10,10 +10,12 @@ import AccountGuard from "@/components/AccountGuard";
 import ThemeSync from "@/components/ThemeSync";
 import RealtimeProvider from "@/components/RealtimeProvider";
 import CodeFoldProvider from "@/components/markdown/CodeFoldProvider";
+import MotionProvider from "@/components/MotionProvider";
 import type { User } from "@/lib/api";
 import { getMeCached, getPublicSettingsCached } from "@/lib/serverData";
 import { TOKEN_COOKIE, authCookieHeader } from "@/lib/cookies";
 import { accentStyleCSS } from "@/lib/theme";
+import { motionConfigFromSettings } from "@/lib/motion";
 
 // 构建期下载并自托管字体：同源加载 + 自动 preload + fallback 度量校正，
 // 消除 F5 时 Google CDN 字体到达后整页"由粗变细"的 FOUT 闪动
@@ -73,6 +75,13 @@ export default async function RootLayout({
   const settings = await getPublicSettingsCached();
   const accent = settings.accent;
   const accentCSS = accentStyleCSS(accent || "");
+  const motionCfg = motionConfigFromSettings(settings);
+  const motionHtmlClass = [
+    !motionCfg.ui_animations ? "j13-reduce-motion" : "",
+    motionCfg.ui_animations && !motionCfg.anim_chrome ? "j13-reduce-chrome" : "",
+  ]
+    .filter(Boolean)
+    .join(" ");
 
   let user: User | null = null;
   let unread = 0;
@@ -89,7 +98,7 @@ export default async function RootLayout({
   return (
     <html
       lang="zh-CN"
-      className={`${theme === "dark" ? "dark" : ""} ${jakarta.variable} ${notoSC.variable} ${jetbrainsMono.variable}`}
+      className={`${theme === "dark" ? "dark" : ""} ${motionHtmlClass} ${jakarta.variable} ${notoSC.variable} ${jetbrainsMono.variable}`.trim()}
     >
       <body className="min-h-screen flex flex-col">
         {accentCSS ? (
@@ -116,12 +125,14 @@ export default async function RootLayout({
           tabIndex={-1}
           className="flex-1 w-full max-w-[1440px] mx-auto px-4 sm:px-6 py-7 sm:py-9 outline-none"
         >
-          <CodeFoldProvider
-            initialEnabled={settings.code_block_auto_fold}
-            initialFoldLines={settings.code_block_fold_lines}
-          >
-            {children}
-          </CodeFoldProvider>
+          <MotionProvider initial={motionCfg}>
+            <CodeFoldProvider
+              initialEnabled={settings.code_block_auto_fold}
+              initialFoldLines={settings.code_block_fold_lines}
+            >
+              {children}
+            </CodeFoldProvider>
+          </MotionProvider>
         </main>
         <Footer siteName={settings.site_name} />
         <Toaster />