Limit motion to one animated element per page (DS-2)

- Course navigation: only the completion percent animates; the
  "N of M lessons" counter is static. NumberFlow is enabled only in the
  visible copy of the navigation (drawer on phones, sidebar otherwise).
- globals.css: disable Vaul drawer and overlay animation under
  prefers-reduced-motion.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

src/app/globals.css

@@ -298,3 +298,14 @@
   margin: 0 0 0.5rem;
 }
 .comment-md pre code { background: none; padding: 0; }
+
+/* DS-2 §8: with prefers-reduced-motion there is no motion at all.
+   Vaul animates the sheet via injected CSS and inline transitions while
+   dragging — !important overrides both, the sheet just appears/disappears. */
+@media (prefers-reduced-motion: reduce) {
+  [data-vaul-drawer],
+  [data-vaul-overlay] {
+    animation: none !important;
+    transition: none !important;
+  }
+}

src/components/student/course-sidebar.tsx

@@ -4,7 +4,7 @@ import Link from "next/link";
 import { usePathname } from "next/navigation";
 import { useState } from "react";
 import { Menu, X } from "lucide-react";
-import NumberFlow, { NumberFlowGroup } from "@number-flow/react";
+import NumberFlow from "@number-flow/react";
 import { AubadeDrawer, ResponsiveDialogTitle } from "@/components/shared/responsive-dialog";
 import { useIsMobile } from "@/hooks/use-media-query";
 
@@ -30,11 +30,14 @@ function CourseNavBody({
   completedLessonIds,
   pathname,
   onNavigate,
+  animateProgress,
 }: {
   course: Course;
   completedLessonIds: Set<string>;
   pathname: string;
   onNavigate: () => void;
+  /** DS-2: one animated moment per page — only the visible copy animates. */
+  animateProgress: boolean;
 }) {
   const totalLessons = course.modules.reduce((s, m) => s + m.lessons.length, 0);
   const completedCount = course.modules
@@ -66,14 +69,18 @@ function CourseNavBody({
         {totalLessons > 0 && (
           <div>
             <div className="flex items-center justify-between mb-1">
-              <NumberFlowGroup>
               <span className="text-xs" style={{ color: "var(--muted-foreground)" }}>
-                  <NumberFlow value={completedCount} respectMotionPreference /> из {totalLessons} уроков
+                {completedCount} из {totalLessons} уроков
               </span>
               <span className="text-xs font-bold" style={{ color: "var(--foreground)" }}>
-                  <NumberFlow value={progressPct} suffix="%" respectMotionPreference />
+                {/* The page's single animated moment (DS-2 §8); static under reduced motion. */}
+                <NumberFlow
+                  value={progressPct}
+                  suffix="%"
+                  animated={animateProgress}
+                  respectMotionPreference
+                />
               </span>
-              </NumberFlowGroup>
             </div>
             <div
               className="h-1.5 w-full"
@@ -207,6 +214,7 @@ export function CourseSidebar({
           completedLessonIds={completedLessonIds}
           pathname={pathname}
           onNavigate={() => setOpen(false)}
+          animateProgress={!isMobile}
         />
       </aside>
 
@@ -218,6 +226,7 @@ export function CourseSidebar({
             completedLessonIds={completedLessonIds}
             pathname={pathname}
             onNavigate={() => setSheetOpen(false)}
+            animateProgress
           />
         </AubadeDrawer>
       )}