feat(previs): 图片生成预演台 - 从图片节点交给 Agent 复现为可编辑 3D 预演

图片工具栏新增「生成预演台」，自动选用支持看图的文本模型并提交复现指令。对话用节点卡片展示「此图」，普通图片演员只写名称时不再要求角色卡绑定。

web/test/agent-chat-node-links.test.tsx

@@ -64,6 +64,23 @@ test("renders an agent node link as a titled inline node card", () => {
     expect(visibleText).not.toContain("video-1790385749473-q4157");
 });
 
+test("renders the image-to-previs user request with the existing canvas node card", () => {
+    const imageReference = { ...videoReference, kind: "image" as const, sourceType: "image" as const, label: "道姑", title: "道姑" };
+    const html = renderToStaticMarkup(
+        <AgentChatMessage
+            item={{ id: "user-previs", role: "user", text: "根据此图生成 3D 预演台", canvasReferenceNodeId: imageReference.nodeId }}
+            theme={canvasThemes.dark}
+            references={[imageReference]}
+            onFocusNode={() => {}}
+        />,
+    );
+
+    expect(html).toContain('class="agent-message-node-link"');
+    expect(html).toContain('class="agent-message-node-link-preview"');
+    expect(html).toContain("道姑");
+    expect(html).toContain("3D 预演台");
+});
+
 test("labels character cards by resource kind instead of the underlying text type", () => {
     const nodeId = "text-1790385749473-char1";
     const reference = { id: nodeId, nodeId, kind: "character" as const, label: "李莫愁", title: "李莫愁", sourceType: "text" as const };