Mastodon clients send plain text — the server must convert bare URLs
and @user@domain mentions into HTML links. Previously, URLs appeared
as plain text and mentions were not stored as mention objects.
- Bare URLs (http/https) are wrapped in <a> tags
- @user@domain patterns are converted to profile links with h-card markup
- Mentions are extracted into the mentions[] array with name and URL
- Only processes content that doesn't already contain <a> tags
(avoids double-linkifying Micropub-rendered content)
94c4546234