feat(canvas): 动效系统与响应式适配 - token落地+断点体系+无障碍 #99

基于 Wayfinder #99 决议，完成动效/响应式/无障碍三大维度落地：

1. 动效 token 迁移（CSS 动画）
   - 33 处 easing 替换为 var(--motion-ease-out/in-out/linear)
   - 7 处有限动画 duration 替换为 var(--motion-dur-*-calc)
     （含 motion-scale 降级，自动联动 prefers-reduced-motion）
   - canvas-node batch 动画内联值替换为 token

2. aceternityMotion 对齐 + motion/react 硬编码替换
   - 添加 JS↔CSS token 映射文档注释
   - 3 处 motion/react 硬编码 duration 替换为 aceternityMotion.* 引用

3. infinite 装饰动画 reduced-motion 降级
   - L1 (prefers-reduced-motion): 缩短至 0.01ms + 单次播放
   - L2 (.no-motion): animation: none 完全禁用
   - 覆盖 9 个 infinite 动画类（连线流光/边框流光/极光标题等）

4. 响应式断点体系
   - @theme 新增 3 断点 token: --breakpoint-tablet(768)/desktop(1024)/wide(1440)
   - 修复 canvas-toolbar 外观面板缺 max-w 导致移动端溢出

5. 无障碍
   - 画布页新增 skip-to-content 链接（键盘用户跳过侧栏直达画布）
   - 任务进度面板 aria-live="polite"（屏幕阅读器播报任务数变化）

Closes #99

web/src/pages/canvas/canvas-project-feedback.tsx

@@ -34,7 +34,7 @@ export function CanvasUploadStatusToast({ status, theme }: { status: CanvasUploa
         >
             <div className="absolute inset-x-0 top-0 h-px" style={{ background: `linear-gradient(90deg, transparent, ${accent}, transparent)` }} />
             <div className="flex items-start gap-3">
-                <motion.span animate={status.done || status.error ? { scale: [0.8, 1.08, 1] } : { y: [0, -2, 0] }} transition={status.done || status.error ? { duration: 0.3 } : { duration: 1.5, repeat: Number.POSITIVE_INFINITY }} className="mt-0.5 grid size-9 shrink-0 place-items-center rounded-[var(--dock-radius)] border" style={{ background: theme.spatial.surface, borderColor: `${accent}44`, color: accent }}>
+                <motion.span animate={status.done || status.error ? { scale: [0.8, 1.08, 1] } : { y: [0, -2, 0] }} transition={status.done || status.error ? { duration: aceternityMotion.duration.panel } : { duration: 1.5, repeat: Number.POSITIVE_INFINITY }} className="mt-0.5 grid size-9 shrink-0 place-items-center rounded-[var(--dock-radius)] border" style={{ background: theme.spatial.surface, borderColor: `${accent}44`, color: accent }}>
                     {status.error ? <TriangleAlert className="size-4" /> : status.done ? <CheckCircle2 className="size-4" /> : <CloudUpload className="size-4" />}
                 </motion.span>
                 <span className="min-w-0 flex-1">

web/src/pages/canvas/project.tsx

@@ -1350,7 +1350,9 @@ function InfiniteCanvasPage() {
     if (!projectLoaded) return <CanvasRefreshShell />;
 
     return (
-        <main className="flex h-full min-h-0 overflow-hidden" style={{ background: theme.canvas.background, color: theme.node.text }}>
+        <>
+        <a href="#canvas-main" className="sr-only focus:not-sr-only focus:absolute focus:left-4 focus:top-4 focus:z-[var(--z-toast)] focus:rounded-md focus:border focus:bg-background focus:px-4 focus:py-2 focus:text-sm focus:font-medium focus:shadow-lg">跳转到画布主内容</a>
+        <main id="canvas-main" tabIndex={-1} className="flex h-full min-h-0 overflow-hidden outline-none" style={{ background: theme.canvas.background, color: theme.node.text }}>
             {currentProject?.projectId ? <CanvasProjectSidebar projectId={currentProject.projectId} detail={linkedProjectQuery.data} onAddChapter={handleProjectChapterInsert} onLocateStyle={locateProjectStyleNode} onOpenAssets={() => openProjectAssets()} /> : null}
             <section className="relative min-w-0 flex-1 overflow-hidden">
                 <CanvasTopBar
@@ -1772,5 +1774,6 @@ function InfiniteCanvasPage() {
                 />
             ) : null}
         </main>
+        </>
     );
 }