fix(single): align cover breadcrumb with the article title

With a featured image the breadcrumb sits under the title inside the cover
overlay, but its first icon started 6px left of the title's left edge.

The overlay rule carried an extra `padding: 0` that this theme added on top of
the reference. The same node also matches `ul.breadcrumb { padding: 0 }`
(0,1,1 specificity), which outranks the base `.breadcrumb { padding: 0 8px }`
(0,1,0) — so the reference's `margin-left: -6px` nudge was applied with no
inset to compensate, pulling the whole row 6px to the left.

Writing the inset back as `padding: 0 8px` on the overlay rule restores the
reference geometry: -6px + 8px nets +2px from the panel edge. The global
`ul.breadcrumb` reset and the video footer variant are untouched, so archive
and video breadcrumbs keep their current padding.

Tests: new case in the single-cover contract suite pins the 8px inset (and the
global reset); cover suite 12/12, widget suite 829/830 with the pre-existing
frontend-lifecycle failure.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>

assets/css/frontend/breadcrumb.css

@@ -69,15 +69,17 @@ ul.breadcrumb > li:last-child,
   color: var(--main-color, var(--color-ink-2, #4e5358));
 }
 
-/* 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。 */
+/* Cover overlay breadcrumb — legacy .single-cover-con：标题叠加封面。
+   只做 -6px 左拉与不透明度还原；padding 需显式给回 0 8px：
+   同一节点的 ul.breadcrumb 重置（padding:0）优先级高于 .breadcrumb，
+   不写回就会让首项图标比标题左移 6px。 */
 .single-cover-con .breadcrumb,
 .single-cover-con ul.breadcrumb,
 .single-cover-con .breadcrumb-nav {
   font-size: 13px;
   margin: 5px 0 0 -6px;
   opacity: unset;
-  padding: 0;
+  padding: 0 8px;
   background: transparent;
 }