fix(web): design1/2 缩略图与 design2 设为背景交互修复

- design1：预览/最近文件缩略图按 background 边界截取，去掉多余白盘
- design2：设为背景贴齐 1012x648 卡框，保存/打开保留用户背景 src
- design2：列表可选中锁定对象并加载完整属性，缩略图叠加 front_bg 模板
- design2：固定卡框锚点，避免选中背景时标尺/蒙版随属性面板漂移

Co-authored-by: Cursor <cursoragent@cursor.com>

frontend-web/js/design1/output.js

@@ -52,6 +52,62 @@ async function saveImageAsPNG(buffer) {
     }
 }
 
+/** 从画布像素截取光盘外接方（含 after:render 圆外暗蒙版），与编辑器所见一致 */
+function soonDesign1CaptureCanvasRect(canvas, outW, outH, format, quality) {
+    var bg = window.background_image1 || window.background_image;
+    if (!canvas || !bg) return '';
+    var srcEl = canvas.lowerCanvasEl;
+    if (!srcEl || !srcEl.getContext) return '';
+    var sx = bg.scaleX == null ? 1 : bg.scaleX;
+    var sy = bg.scaleY == null ? 1 : bg.scaleY;
+    var sw = bg.width * sx;
+    var sh = bg.height * sy;
+    var retina = (typeof canvas.getRetinaScaling === 'function') ? canvas.getRetinaScaling() : 1;
+    outW = outW || Math.round(sw);
+    outH = outH || Math.round(sh);
+    var tmp = document.createElement('canvas');
+    tmp.width = outW;
+    tmp.height = outH;
+    var tctx = tmp.getContext('2d');
+    tctx.drawImage(
+        srcEl,
+        bg.left * retina, bg.top * retina, sw * retina, sh * retina,
+        0, 0, outW, outH
+    );
+    if (format === 'jpeg') return tmp.toDataURL('image/jpeg', quality == null ? 0.75 : quality);
+    return tmp.toDataURL('image/png');
+}
+
+function soonBuildDesign1SavePreviewPic(canvas) {
+    var THUMB_MAX = 102400;
+    var c1 = window.canvas1;
+    if (!canvas || (c1 && canvas !== c1)) return '';
+    var hidden = [];
+    canvas.getObjects().forEach(function (obj) {
+        if (obj.isGuideLine) {
+            hidden.push(obj);
+            obj.visible = false;
+        }
+    });
+    if (canvas.discardActiveObject) canvas.discardActiveObject();
+    canvas.renderAll();
+
+    var url = '';
+    var sizes = [320, 280, 240, 200];
+    var quals = [0.82, 0.68, 0.52, 0.38];
+    for (var i = 0; i < sizes.length; i++) {
+        url = soonDesign1CaptureCanvasRect(canvas, sizes[i], sizes[i], 'jpeg', quals[i]);
+        if (url && url.indexOf('data:image/') === 0 && url.length <= THUMB_MAX) break;
+        url = '';
+    }
+
+    hidden.forEach(function (obj) { obj.visible = true; });
+    canvas.renderAll();
+    if (canvas.requestRenderAll) canvas.requestRenderAll();
+    return url;
+}
+window.soonBuildDesign1SavePreviewPic = soonBuildDesign1SavePreviewPic;
+
 window.display_func = function display_func(img1, img2, img3) {
     $("#base_control").hide();
     $("#line_control").hide();
@@ -217,13 +273,18 @@ window.display_func = function display_func(img1, img2, img3) {
         left: all_left
     });
 
-    g3.push(img1);
-    let url3 = new fabric.Group(g3).toDataURL({
-        height: 2787,
-        width: 2787,
-        top: all_top,
-        left: all_left
+    var hiddenForPreview = [];
+    canvas1.getObjects().forEach(function (o) {
+        if (o.isGuideLine) {
+            hiddenForPreview.push(o);
+            o.visible = false;
+        }
     });
+    canvas1.discardActiveObject();
+    canvas1.renderAll();
+    let url3 = soonDesign1CaptureCanvasRect(canvas1, 2787, 2787, 'png');
+    hiddenForPreview.forEach(function (o) { o.visible = true; });
+    canvas1.renderAll();
     let url5 = new fabric.Group(g5).toDataURL({
         height: 2787,
         width: 2787,