fix(05-02): single dark theme for code blocks — github-dark always, remove dual-theme CSS

app/assets/css/main.css

@@ -7,15 +7,9 @@
   scroll-margin-top: 5rem;
 }
 
-/* Code blocks: always dark regardless of color mode.
-   ProsePre wrapper owns the background (#0d1117).
-   Target pre span directly — .shiki class is absent when ProsePre overrides <pre>. */
-.shiki, pre span {
-  color: var(--shiki-dark) !important;
+/* Code blocks: single dark theme (github-dark), background transparent — ProsePre div owns #0d1117 */
+pre span {
   background-color: transparent !important;
-  font-style: var(--shiki-dark-font-style) !important;
-  font-weight: var(--shiki-dark-font-weight) !important;
-  text-decoration: var(--shiki-dark-text-decoration) !important;
 }
 
 @theme {

nuxt.config.ts

@@ -67,10 +67,7 @@ export default defineNuxtConfig({
     build: {
       markdown: {
         highlight: {
-          theme: {
-            default: 'github-light',
-            dark: 'github-dark'
-          },
+          theme: 'github-dark',
           langs: ['kotlin', 'java', 'typescript', 'shell', 'bash', 'json', 'vue', 'html', 'css']
         }
       }