Fix StandardRB lint: use match? instead of =~

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

Author: dariye

lib/llms_txt_generator.rb

@@ -89,7 +89,7 @@ def extract_header(file_path)
       title = $1 || $2 || $3
       description = $4
       # If title is a variable reference (like `component`), resolve it
-      if title =~ /\A[a-z_]+\z/
+      if title.match?(/\A[a-z_]+\z/)
         content.match(/#{title}\s*=\s*"([^"]+)"/) { |m| title = m[1] }
       end
       [title, description]