feat: copy saved file path to clipboard after local save

After writing the screenshot to disk, copy its path to the clipboard so
it can be pasted immediately, matching the upload and summary flows. The
save status now shows the copied path. A clipboard error does not fail
the save itself.

app.go

@@ -343,7 +343,7 @@ func (a *App) runSaveImagePipeline(pngBytes []byte, dir string) (string, error)
 		wruntime.EventsEmit(a.ctx, "upload:failure", err.Error())
 		return "", err
 	}
-	a.emitOperationStatus("save", "保存完成", path, "success")
+	a.emitOperationStatus("save", "保存完成", "文件路径已复制到剪贴板："+path, "success")
 	wruntime.EventsEmit(a.ctx, "upload:success", path)
 	return path, nil
 }