Dave Morin
87bf3debcc
Without this entry, the planner's _default_sources_for_intent() drops
xquik from the candidate pool for how_to / comparison / news intents
because SOURCE_CAPABILITIES.get("xquik", set()) returns the empty set.
Users with XQUIK_API_KEY set get zero Xquik results even though the
engine recognizes the key.
Mirrors the capabilities for "x" since both are X/Twitter-shaped
discussion + social sources.
Fixes #319