fix(canvas): 人物质感变体自动触发生成，修复缩略图不变 #91 (#92)

- use-canvas-media-tools.ts: createPortraitTextureNode 改为 generatePortraitTextureNode，
  节点创建后立即触发后端生成任务（与情绪/多视角/局部编辑保持一致）：
  使用 nodeReferenceImage 获取源图引用，buildPortraitTexturePrompt 构建提示词，
  runBackendCanvasGenerationTask 执行生成，完成后更新缩略图
- project.tsx: 同步重命名 createPortraitTextureNode → generatePortraitTextureNode
- canvas-drawing-excalidraw-editor.tsx: getDimensions 参数补充 number 类型注解
- canvas-drawing-editor-modal.tsx: Pick 类型补充 engine 字段

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

web/src/components/canvas/canvas-drawing-editor-modal.tsx

@@ -16,7 +16,7 @@ type CanvasDrawingEditorModalProps = {
     projectId: string;
     node: CanvasNodeData | null;
     onClose: () => void;
-    onSaved: (nodeId: string, summary: Pick<CanvasDrawingSnapshot, "revision" | "updatedAt" | "shapeCount" | "pageCount">) => void;
+    onSaved: (nodeId: string, summary: Pick<CanvasDrawingSnapshot, "engine" | "revision" | "updatedAt" | "shapeCount" | "pageCount">) => void;
 };
 
 export function CanvasDrawingEditorModal({ open, projectId, node, onClose, onSaved }: CanvasDrawingEditorModalProps) {