Fix syntax highlighting CSS disappearing in watch mode

Import syntax-highlighting.css directly in tailwind.css instead of
appending it via cat command in build-css script. This ensures
syntax highlighting is preserved when using watch-css.

Fixes #255

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

Author: taea

package.json

@@ -3,7 +3,7 @@
   "version": "1.0.0",
   "description": "Ruby Language Website Renewal with Tailwind CSS",
   "scripts": {
-    "build-css": "tailwindcss -i ./stylesheets/tailwind.css -o ./stylesheets/compiled.css && cat ./stylesheets/components/syntax-highlighting.css >> ./stylesheets/compiled.css",
+    "build-css": "tailwindcss -i ./stylesheets/tailwind.css -o ./stylesheets/compiled.css",
     "watch-css": "tailwindcss -i ./stylesheets/tailwind.css -o ./stylesheets/compiled.css --watch"
   },
   "devDependencies": {