feat(canvas): 沉浸专注与短剧流程 - 支持专注模式与流程条并入顶栏体系 (#157)

- 沉浸专注：进入后隐藏顶部栏、Dock、缩放控件、小地图与素材托盘，保留专注胶囊可唤出工具与智能体；小屏默认进入，⇧⌘F 切换，Esc 在无选中与浮层时退出
- 智能体面板改贴边停靠并按顶栏让位，作为沉浸专注的配套依赖
- 短剧流程条并入顶栏：折叠入口移入顶栏按钮组，展开条锚定顶栏下缘，与工作模式开关互斥
- 流程步骤改为里程碑节点与状态轨道，新增 --flow-step-* Design Token

Co-authored-by: sikongyue <3155157671@qq.com>

web/src/components/canvas/canvas-context-menu.tsx

@@ -140,6 +140,7 @@ export function CanvasNodeContextMenu({
         <>
             <SpotlightSurface
                 spotlightColor={theme.toolbar.itemHover}
+                data-canvas-context-menu
                 initial={reducedMotion ? { opacity: 0 } : { opacity: 0, scale: 0.97, x: -3, y: -3 }}
                 animate={{ opacity: 1, scale: 1, x: 0, y: 0 }}
                 transition={{ duration: aceternityMotion.duration.instant, ease: aceternityMotion.easing.enter }}