feat(canvas): 多图批次 - 子图操作条补齐（下载/副本/设主图/失败重试删除）

- 展开批次子图悬浮操作条：成功子项下载/创建副本/设为主图，失败子项重试/删除
- 批次主图位常驻下载按钮
- 通过 CanvasNodeActionContext 注入画布级动作（download/duplicate/delete），不改 world-layers 数据模型

web/src/pages/canvas/project.tsx

@@ -80,6 +80,7 @@ import { CanvasProjectMediaDialogs } from "./canvas-project-media-dialogs";
 import { CanvasProjectSelectionToolbar } from "./canvas-project-selection-toolbar";
 import { CanvasProjectStatusDialogs } from "./canvas-project-status-dialogs";
 import { CanvasProjectWorldLayers } from "./canvas-project-world-layers";
+import { CanvasNodeActionContext } from "@/components/canvas/canvas-node-action-context";
 import { CanvasRefreshShell } from "./canvas-refresh-shell";
 import type { CanvasImageEmotionPayload } from "@/components/canvas/canvas-node-emotion-panel";
 import { CanvasEmotionWorkspace } from "@/components/canvas/canvas-emotion-workspace";
@@ -1779,6 +1780,7 @@ function InfiniteCanvasPage() {
                                 onFileDragLeave={handleFileDragLeave}
                                 onFileDragOver={handleFileDragOver}
                             >
+                                <CanvasNodeActionContext.Provider value={{ download: downloadNodeImage, duplicate: (node) => duplicateNode(node.id), deleteNode: (node) => deleteNodes(new Set([node.id])) }}>
                                 <CanvasProjectWorldLayers
                                     projectId={projectId}
                                     viewportScale={viewport.k}
@@ -1847,6 +1849,7 @@ function InfiniteCanvasPage() {
                                     onOpenDrawing={openDrawingNode}
                                     onStartBatchConnection={startBatchConnection}
                                 />
+                                </CanvasNodeActionContext.Provider>
                             </InfiniteCanvas>
 
                             <CanvasActiveTaskPanel tasks={activeTasks} topInset={focusMode ? "var(--space-3)" : "var(--canvas-topbar-offset)"} />