fix(single): restore Zibll float dual-column and article chrome

Align single-post layout/visuals with Zibll: fix sidebar-over-content
float geometry (position:unset, 311px token, kill Bootstrap/container
padding and the 280px sidebar override), demote theme-box to spacing-
only, unify breadcrumb/cover/graphic utilities, and split aksrt-single
render helpers under the file-size limit.

assets/css/frontend/single-post/content.css

@@ -1,9 +1,34 @@
 /* ========== Single Post ========== */
+
+/* Zibll .article — card body padding wins over .box-body (main.css order) */
+.article,
+article.article.box-body,
+.article.main-bg.box-body {
+  padding: 0 30px;
+  overflow: hidden;
+}
+
+@media (max-width: 767px) {
+  .article,
+  article.article.box-body,
+  .article.main-bg.box-body {
+    padding: 0 15px;
+  }
+
+  .article-header .article-title {
+    font-size: 18px;
+  }
+}
+
 .entry-header,
 .article-header {
   margin-bottom: 10px;
   padding-bottom: 0;
   border-bottom: none;
+  /* theme-box is spacing only — never paint a nested card here */
+  background: transparent;
+  box-shadow: none;
+  border-radius: 0;
 }
 
 /* 标题 — 对齐 zibll: 22px, bold, line-height 1.4 */
@@ -17,6 +42,10 @@
   color: var(--key-color, var(--color-ink));
 }
 
+.article-title > a:hover {
+  color: inherit;
+}
+
 .article-header .article-title {
   font-size: 22px;
   font-weight: bold;