feat: 代码块语法高亮 + 语言选择 + 样式统一

- 引入 @tiptap/extension-code-block-lowlight + lowlight 实现代码语法高亮
- 工具栏新增语言下拉选择器，光标在代码块内时显示，支持 27 种常用语言
- 默认语言 text，高亮主题适配 MetaLab 深蓝背景 (#1a2332)
- 代码块语言标签用 JS 动态注入 DOM 元素（避免 ::before 在 overflow 容器中失效）
- 详情页同步代码块高亮和语言标签显示
- 编辑器与详情页样式统一：代码块暗色背景、引用蓝色边框、链接 accent 蓝
- sanitizePolicy 放行 data-language 属性和 hljs-* class
- 修复 import map 避免 keyed plugin 重复实例
- 修复详情页代码块开头空白行（移除多余的 padding-top）
- 修复语法错误（多余的闭合括号）

templates/MetaLab-2026/static/css/posts.css

@@ -128,9 +128,9 @@
 /* 代码块基础样式 */
 .post-detail-body pre {
     position: relative;
-    background: #f3f4f6;
+    background: #1a2332;
+    color: #e2e8f0;
     padding: 12px 16px;
-    padding-top: 36px;
     border-radius: 8px;
     overflow-x: auto;
     font-size: 14px;
@@ -138,19 +138,21 @@
     font-family: 'Menlo', 'Consolas', 'Monaco', 'Liberation Mono', monospace;
 }
 
-/* 通过 JS 动态注入语言标签，因为 CSS attr() 无法从 class 中提取 */
-.code-lang-label {
+/* 代码块语言标签（JS 动态注入） */
+.post-detail-body pre .code-lang-label {
     position: absolute;
     top: 0;
     left: 0;
     right: 0;
-    padding: 8px 16px !important;
-    background: #e5e7eb;
-    color: #6b7280;
+    padding: 4px 16px;
     font-size: 11px;
     font-weight: 600;
+    color: #94a3b8;
+    background: #2c3e50;
     border-radius: 8px 8px 0 0;
     font-family: -apple-system, BlinkMacSystemFont, 'Segoe UI', 'Helvetica Neue', Arial, sans-serif;
+    pointer-events: none;
+    z-index: 1;
 }
 
 .post-detail-body pre code {
@@ -158,6 +160,8 @@
     border: none !important;
     padding: 0 !important;
     font-size: inherit !important;
+    white-space: pre;
+    display: block;
 }
 
 .post-detail-body code {
@@ -167,6 +171,43 @@
     font-size: 0.9em;
 }
 
+/* highlight.js 语法高亮 — 适配 MetaLab 深蓝背景 */
+.post-detail-body pre code .hljs-keyword,
+.post-detail-body pre code .hljs-selector-tag,
+.post-detail-body pre code .hljs-literal,
+.post-detail-body pre code .hljs-section,
+.post-detail-body pre code .hljs-link { color: #c792ea; }
+.post-detail-body pre code .hljs-string,
+.post-detail-body pre code .hljs-title,
+.post-detail-body pre code .hljs-name,
+.post-detail-body pre code .hljs-type,
+.post-detail-body pre code .hljs-attribute,
+.post-detail-body pre code .hljs-symbol,
+.post-detail-body pre code .hljs-bullet,
+.post-detail-body pre code .hljs-addition,
+.post-detail-body pre code .hljs-variable,
+.post-detail-body pre code .hljs-template-tag,
+.post-detail-body pre code .hljs-template-variable { color: #c3e88d; }
+.post-detail-body pre code .hljs-comment,
+.post-detail-body pre code .hljs-quote,
+.post-detail-body pre code .hljs-deletion,
+.post-detail-body pre code .hljs-meta { color: #676e95; }
+.post-detail-body pre code .hljs-number,
+.post-detail-body pre code .hljs-regexp,
+.post-detail-body pre code .hljs-built_in { color: #f78c6c; }
+.post-detail-body pre code .hljs-function .hljs-title,
+.post-detail-body pre code .hljs-doctag,
+.post-detail-body pre code .hljs-formula { color: #82aaff; }
+.post-detail-body pre code .hljs-tag,
+.post-detail-body pre code .hljs-subst { color: #f07178; }
+.post-detail-body pre code .hljs-emphasis { font-style: italic; }
+.post-detail-body pre code .hljs-strong { font-weight: bold; }
+.post-detail-body pre code .hljs-attr,
+.post-detail-body pre code .hljs-selector-attr,
+.post-detail-body pre code .hljs-selector-class,
+.post-detail-body pre code .hljs-selector-id,
+.post-detail-body pre code .hljs-selector-pseudo { color: #ffcb6b; }
+
 .post-detail-body img {
     max-width: 100%;
     height: auto;