Add PinnedArticleService that always returns configured Naver articles
first to the front-end. Articles are built from a bare URL via a new
NewsApiClient.buildArticleFromUrl (OG/meta parsing + existing content and
image-localization pipeline), cached to disk with a TTL, and prepended
with de-duplication in NewsStorageService. Configurable via
NEWS_PINNED_ARTICLE_URLS / NEWS_PINNED_CATEGORIES / NEWS_PINNED_TTL_MS.
Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
