fix(canvas): 复制粘贴与生成占位 - 系统图片优先并按比例显示占位框 (#45)

- 粘贴优先系统剪贴板图片，复制节点时写入标记避免旧图片抢占
- 粘贴/复制节点清理批次绑定，并补回参考图入边
- 生成中图片占位按设置比例显示
- Nano Banana / Imagen / Veo / Omni 匹配 Gemini 图标

Co-authored-by: Danborad <Danborad@users.noreply.github.com>

web/src/lib/canvas/canvas-node-size.ts

@@ -6,10 +6,14 @@ export function fitNodeSize(width: number, height: number, maxWidth = 640, maxHe
 }
 
 export function nodeSizeFromRatio(size: string, baseWidth: number, baseHeight: number) {
-    const match = size?.match(/^(\d+)(?:x|:)(\d+)/);
+    const raw = String(size || "").trim();
+    if (!raw || raw.toLowerCase() === "auto") return null;
+    // 支持 16:9 / 1024x576 / 16:9-2k
+    const match = raw.match(/^(\d+(?:\.\d+)?)(?:x|:)(\d+(?:\.\d+)?)/i);
     if (!match) return null;
     const width = Number(match[1]);
     const height = Number(match[2]);
+    if (!Number.isFinite(width) || !Number.isFinite(height) || width <= 0 || height <= 0) return null;
     const ratio = width / Math.max(1, height);
     if (ratio < 0.25 || ratio > 4) return { width: baseWidth, height: baseHeight };
     return ratio >= baseWidth / baseHeight ? { width: baseWidth, height: baseWidth / ratio } : { width: baseHeight * ratio, height: baseHeight };