fix @handle URLs to use /@handle paths + add ac-news edit command
- renderHandle and autoLinkHandles now link to /@username (not /username)
- new `ac-news edit <code>` CLI command with:
--title, --body, --url, --editor, --replace/--with, --dry-run
Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>