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/MotionProvider.tsx

@@ -0,0 +1,52 @@
+"use client";
+
+import { useEffect, type ReactNode } from "react";
+import {
+  applyMotionSiteConfig,
+  getMotionSiteConfig,
+  motionConfigFromSettings,
+  type MotionSiteConfig,
+} from "@/lib/motion";
+import { realtime, RT_SETTINGS_CHANGED, type RtSettingsData } from "@/lib/realtime";
+
+/**
+ * 根布局注入：SSR 初值写入 motion 模块 + html class；settings:changed 热更新。
+ */
+export default function MotionProvider({
+  initial,
+  children,
+}: {
+  initial: MotionSiteConfig;
+  children: ReactNode;
+}) {
+  useEffect(() => {
+    applyMotionSiteConfig(motionConfigFromSettings(initial));
+  }, [initial]);
+
+  useEffect(() => {
+    return realtime.on<RtSettingsData>(RT_SETTINGS_CHANGED, (data) => {
+      if (!data) return;
+      const cur = getMotionSiteConfig();
+      applyMotionSiteConfig(
+        motionConfigFromSettings({
+          ui_animations:
+            typeof data.ui_animations === "boolean"
+              ? data.ui_animations
+              : cur.ui_animations,
+          anim_code_fold:
+            typeof data.anim_code_fold === "boolean"
+              ? data.anim_code_fold
+              : cur.anim_code_fold,
+          anim_smooth_scroll:
+            typeof data.anim_smooth_scroll === "boolean"
+              ? data.anim_smooth_scroll
+              : cur.anim_smooth_scroll,
+          anim_chrome:
+            typeof data.anim_chrome === "boolean" ? data.anim_chrome : cur.anim_chrome,
+        })
+      );
+    });
+  }, []);
+
+  return children;
+}