fix(single): close remaining live gaps vs Zibll demo

Align runtime --sidebar-width (300→311), --main-radius, and
body.nav-fixed 88px reserve; enqueue single-post CSS parts directly;
match Zibll action buttons and author avatar DOM; tighten dual-column
tokens after comparing blog.rutua.cn with demo.zibll.com.

assets/css/frontend/base.css

@@ -133,12 +133,13 @@ main.container,
   }
 }
 
-/* Soft pad only when the float dual-column is collapsed */
+/* Soft pad only when the float dual-column is collapsed.
+ * Match Zibll bootstrap container pad (15px) rather than 10px. */
 @media (max-width: 991.98px) {
   .container,
   main.container {
-    padding-right: 10px;
-    padding-left: 10px;
+    padding-right: 15px;
+    padding-left: 15px;
   }
 }
 
@@ -147,8 +148,8 @@ main.container,
   main.container {
     width: 100%;
     max-width: 100%;
-    padding-right: 10px;
-    padding-left: 10px;
+    padding-right: 15px;
+    padding-left: 15px;
   }
 }