Add Wikimedia Commons support using QLever endpoint

Wikimedia Commons also has structured data,
and while its Query Service requires authentication
and is thus unusable, the dataset is available on QLever.

When the site URL points to commons.wikimedia.org,
force the QLever wikimedia-commons endpoint for SPARQL queries.

Commons SDC uses the same Wikidata property URIs
so no query changes are needed.

The get_qlever_ui_url helper now resolves the correct QLever
UI URL based on the site, so query links point to the right
QLever dataset.

Bug: T294893