Two fixes:
- _find_article_md() scans _ARTICLES_DIR for files whose frontmatter
slug matches, so padel-halle-bauen-de.md is found for slug
'padel-halle-bauen'. The previous exact-name lookup missed any file
where the filename ≠ slug (e.g. {slug}-{lang}.md naming convention).
- Editor pane: replace dark navy background with warm off-white (#FEFDFB)
and dark text so it reads like a document, not a code editor.