fix(single): align article code blocks with the reference theme

The article body ran two highlighting pipelines at once: the runtime
EnlighterJS pass (same one the comment area uses) plus a bespoke
precode.js enhancer, and a hand-rolled .code-block skin. The two
disagreed, so rendered blocks carried a dark #282c34 card with 15px
padding, 14px text, a border and a second copy button stacked on top of
the EnlighterJS toolbar.

Drop the parallel path and let one pipeline own code blocks:
- delete precode.js, single-post/code-blocks.css and the unused
  assets/js/enlighter copy that only precode.js referenced
- drop the now-dead has_code requirement (PHP scan + feature enqueue)
- render pre exactly as the reference does: bootstrap's pre box
  (9.5px padding / 13px / radius 4) plus main.css's muted background,
  with the EnlighterJS theme supplying the skin

Also scope the inline-code skin to :not(pre code) so it stops painting
the block background pink, and remap the toolbar copy glyph: \f0ea is
the clipboard in FA4 but "paste" in FA5; the clipboard is \f328.

Verified against the reference at 1440px both themes: pre 13px/18.57,
9.5px padding, radius 4, muted background; EnlighterJS block heights
151.31 / 60.38 match exactly.

assets/css/core/typography.css

@@ -107,28 +107,28 @@ h6 { font-size: 14px; }
   font-size: 0.9em;
 }
 
-/* ===== 代码块 — 对齐 legacy ===== */
-.wp-posts-content pre,
+/* 代码块容器版式由 bootstrap 的 pre 与 main.css 的 .wp-posts-content 规则提供，
+ * 高亮皮肤由 EnlighterJS 自带主题负责，此处不再叠加二次容器。
+ * 静态页用 .entry-content 包装，这里镜像同一组 pre 规则保持两边一致。 */
 .entry-content pre,
 .prose pre {
-  position: relative;
-  background: #282c34;
-  color: #abb2bf;
-  padding: 15px;
-  border-radius: var(--main-radius, 8px);
-  overflow-x: auto;
-  font-size: 14px;
-  line-height: 1.5;
-  margin: 0 0 20px;
+  background: var(--muted-border-color);
+  color: var(--main-color);
 }
 
-.wp-posts-content pre code,
-.entry-content pre code,
-.prose pre code {
-  color: inherit;
-  background: none;
+.entry-content pre:not(.wp-block-code),
+.prose pre:not(.wp-block-code) {
+  border: none;
+  background: 0 0;
   padding: 0;
-  font-size: inherit;
+  margin: 0;
+}
+
+.entry-content .wp-block-code code,
+.prose .wp-block-code code {
+  color: inherit;
+  background-color: unset;
+  margin: unset;
 }
 
 /* ===== 表格 — 对齐 legacy line 8897 ===== */