feat(pay): mirror reference resource row with copy, icon and reorder

The post editor's download row only exposed address / button text / remark,
leaving copy_key, copy_val and class as hidden inputs with no UI, so the
reference copy area, custom button icon, text and color were unreachable.
The submission popup already emitted those keys, which made the two write
paths diverge from anything the editor could produce.

Expose the full reference field set (地址/备注/复制名称/复制内容/图标/文案/
颜色) as an accordion card with drag reordering, add the one genuinely new
`icon` key through aksrt_sanitize_icon_value(), and teach both frontend
download renderers to consume the fields they previously ignored.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

assets/css/frontend/resource-meta/part.css

@@ -1071,6 +1071,30 @@
     background: linear-gradient(135deg, #333333 0%, #1a1a1a 100%);
 }
 
+/* 后台自定义按钮配色：元素同时带 legacy .but 的 b-*/jb-* 类，
+   它们提供 --this-bg / --this-color，这里读取即可覆盖云服务渐变 */
+.resource-download-box__btn--custom {
+    background: var(--this-bg, var(--color-primary, #3B82F6));
+    color: var(--this-color, #fff);
+}
+
+.resource-download-box__btn--custom:hover {
+    background: var(--this-bg, var(--color-primary-active, #2563EB));
+    color: var(--this-color, #fff);
+    filter: brightness(0.94);
+}
+
+.resource-download-box__btn--custom .resource-download-box__service-badge {
+    background: rgb(255 255 255 / 25%);
+}
+
+/* 移动端下载条的 hover 规则作用域更窄，同作用域再声明一次以保持自定义色 */
+.resource-mobile-download-bar .resource-download-box__btn--custom:hover {
+    background: var(--this-bg, var(--color-primary-active, #2563EB));
+    color: var(--this-color, #fff);
+    filter: brightness(0.94);
+}
+
 /* 云服务徽章 */
 .resource-download-box__service-badge {
     display: inline-block;