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-excalidraw-editor.tsx

@@ -31,7 +31,7 @@ export const CanvasDrawingExcalidrawEditor = forwardRef<CanvasDrawingEditorHandl
                 files,
                 mimeType: "image/png",
                 exportPadding: DRAWING_RENDER_PADDING,
-                getDimensions: (width, height) => {
+                getDimensions: (width: number, height: number) => {
                     const scale = Math.min(4, DRAWING_RENDER_MAX_DIMENSION / Math.max(1, width, height));
                     outputWidth = Math.max(1, Math.round(width * scale));
                     outputHeight = Math.max(1, Math.round(height * scale));