fix(report): restore the centered plus icon in the image upload box

main.css already ships the reference plus icon (.preview .add:before/:after,
25px rounded bars centered via inset:0 + margin:auto). The duplicate
left/top:50% + translate version in modal-runtime.css over-constrained
the same pseudo elements (right/bottom:0 + margin:auto from main.css
still applied), pushing the bars to 75%/75% so only an L-shaped corner
was visible. Drop the duplicate and lock the single-source contract in
the report test.

assets/css/frontend/modal-runtime.css

@@ -389,25 +389,10 @@ body.aksrt-modal-runtime-open {
   cursor: pointer;
 }
 
-:is(.order-comment-from, .aksrt-report-modal) .form-upload .preview .add::before,
-:is(.order-comment-from, .aksrt-report-modal) .form-upload .preview .add::after {
-  content: "";
-  position: absolute;
-  left: 50%;
-  top: 50%;
-  background: var(--color-ink-3, #9ca3af);
-  transform: translate(-50%, -50%);
-}
-
-:is(.order-comment-from, .aksrt-report-modal) .form-upload .preview .add::before {
-  width: 22px;
-  height: 2px;
-}
-
-:is(.order-comment-from, .aksrt-report-modal) .form-upload .preview .add::after {
-  width: 2px;
-  height: 22px;
-}
+/* 加号图标不在此重复定义：main.css 已有参考主题原生实现
+   （.preview .add:before/:after —— 25px 圆角杠，inset:0 + margin:auto 居中）。
+   此前这里的 left/top:50% + translate 版本与该规则叠加导致过约束，
+   加号被推到 75%/75% 只剩“L”形，故整体删除、统一走主样式包。 */
 
 :is(.order-comment-from, .aksrt-report-modal) .form-upload .preview .preview-item img {
   width: 100%;