- Add language selector (en/de) to article create/edit form
- Store language and generated seo_head in articles table on CREATE and UPDATE
- Write HTML build to BUILD_DIR/{lang}/{slug}.html (consistent with pSEO)
- article_detail.html: render article.seo_head when present (canonical,
hreflang, OG, JSON-LD Article) — falls back to inline for legacy articles
Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>