fix(single): place the video footer breadcrumb like the reference

Drop the invented .post-breadcrumbs wrapper and echo the breadcrumb
inside the reference's flex jsb at row; split .single-video .breadcrumb
out of the cover-overlay rule (-6px pull and opacity reset belong to
title-over-cover contexts only) and restore the legacy 15px footer
padding. Pin the structure in the cover contract test and rebuild the
homepage aggregates.

assets/css/frontend/breadcrumb.css

@@ -69,12 +69,11 @@ ul.breadcrumb > li:last-child,
   color: var(--main-color, var(--color-ink-2, #4e5358));
 }
 
-/* Cover / video footer breadcrumb — legacy single-cover-con / single-video */
+/* Cover overlay breadcrumb — legacy .single-cover-con：标题叠加封面，
+   面包屑需要 -6px 左拉与不透明度还原。 */
 .single-cover-con .breadcrumb,
 .single-cover-con ul.breadcrumb,
-.single-cover-con .breadcrumb-nav,
-.post-breadcrumbs .breadcrumb,
-.single-video .breadcrumb {
+.single-cover-con .breadcrumb-nav {
   font-size: 13px;
   margin: 5px 0 0 -6px;
   opacity: unset;
@@ -82,6 +81,9 @@ ul.breadcrumb > li:last-child,
   background: transparent;
 }
 
+/* Video footer breadcrumb — legacy .single-video .breadcrumb：标题在下方
+   footer（flex jsb at 行）不叠加封面，只归零内边距，保留基础弱化样式
+   （opacity .6 与 12px 下边距），对齐 zibll main.css。 */
 .single-video .breadcrumb {
   padding: 0;
 }