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/author-actions.css

@@ -457,10 +457,14 @@ html.dark .post-drop-meta__item:hover {
   width: 100%;
 }
 
+.article-avatar .avatar-img {
+  --this-size: 42px;
+}
+
 .article-avatar .avatar-img img,
 .article-avatar .avatar {
-  width: 42px;
-  height: 42px;
+  width: 100%;
+  height: 100%;
   border-radius: 50%;
   object-fit: cover;
 }
@@ -472,6 +476,8 @@ html.dark .post-drop-meta__item:hover {
 
 .article-header .article-avatar .relative {
   margin-top: 20px;
+  position: relative;
+  min-height: 1px;
 }
 
 .single-metabox {
@@ -514,11 +520,9 @@ html.dark .post-drop-meta__item:hover {
   --body-bg-color: rgba(0, 0, 0, 0.3);
 }
 
-.line-form-line {
+/* line-form-line owned by zibll-utilities.css — only context here */
+.article-avatar .line-form-line {
   display: block;
-  height: 1px;
-  background: var(--main-border-color, rgba(50,50,50,.06));
-  margin: 12px 0 0;
 }
 
 .post-actions {