Update URL matching to recognize xiaohongshu explore URLs in addition
to discovery/item links so shared text that uses either format is
handled. Normalize any matched /explore/ paths to /discovery/item/ so
downstream code receives a consistent canonical URL format. This fixes
cases where explore-style links were previously ignored and simplifies
further processing by unifying URL shapes.
Add a second matching branch in extractURL to detect desktop/web
Xiaohongshu links (https://www.xiaohongshu.com/discovery/item/ID)
in addition to existing mobile xhslink short URLs. Try mobile link
first, fall back to web pattern, and return null if neither match.
This improves URL extraction accuracy for shared texts containing
full site links so downstream processing can handle both link forms.
