refactor: Add YouTube link handling for Nexus BBCode format in Markdown to BBCode conversion

Author: chemodun

markdown_to_bbcode.py

@@ -118,6 +118,9 @@ def replace_links(match):
         if bbcode_type == 'steam' and 'youtube.com/watch?v=' in link_url:
             video_id = re.search(r'v=([^&]+)', link_url).group(1)
             return f"[previewyoutube={video_id};full][/previewyoutube]"
+        elif bbcode_type == 'nexus' and 'youtube.com/watch?v=' in link_url:
+            video_id = re.search(r'v=([^&]+)', link_url).group(1)
+            return f"[youtube]{video_id}[/youtube]"
         elif repo_name and not re.match(r'^https?://', link_url):
             absolute_url = f"https://github.com/{repo_name}/raw/main/{relative_path}/{link_url}"
             return f"[url={absolute_url}]{link_text}[/url]"