v0.4.2 — v1.5.6 line marker (retroactive)

Marks the commit the community registry has been serving as urlpattern 0.4.2.

This tag is retroactive: the descriptor published version 0.4.2 from this commit,
but no v0.4.2 tag existed, so the v1.5-line release point was only findable as a
bare SHA. Created ahead of DuckDB 2.0.0 (2026-10-21), after which the registry's
ref field targets the v2.0 line and v1.5 builds move to the new variegata
field — which needs a findable commit for any v1.5.6 bugfix release.

No code change; this is the same tree the registry already serves.