Added standalone Result[T] (frozen+slots, ok/err classmethods, is_ok) to error_types.py per canonical AND-over-OR error_handling.md (not the video_analysis _Ok|_Err sum type). render_markdown renders YAML front-matter from root post, per-post ## sections with reply markers, quote blockquotes, and ./media/<name> links; media_names mapping keeps render decoupled from download_media. TDD: red (no Result) -> green (7 render + 9 types passed).
