Add build-css task as prerequisite for build and serve

Since compiled.css is no longer in the repository, rake build and
rake serve need to generate it first. This also covers rake test
which depends on build.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

Author: hsbt

Rakefile

@@ -13,18 +13,23 @@ CONFIG = "_config.yml"
 
 task default: [:build]
 
+desc "Build CSS with Tailwind"
+task :"build-css" do
+  sh "npm run build-css"
+end
+
 desc "Run tests (test-linter, lint, build)"
 task test: %i[test-news-plugin test-html-lang-plugin test-linter lint build]
 
 desc "Build the Jekyll site"
-task :build do
+task build: :"build-css" do
   require "jekyll"
 
   Jekyll::Commands::Build.process({})
 end
 
 desc "Serve the Jekyll site locally"
-task :serve do
+task serve: :"build-css" do
   require "jekyll"
 
   Jekyll::Commands::Serve.process({})