Replace single-layer fade-out/swap/fade-in with a dual-layer (A/B)
cross-fade so old hexagons dissolve while new ones appear simultaneously.
Pans still do a direct data swap on the active layer since hex positions
are origin-anchored and stable.
Fix click/hover handlers to query both layers via queryRenderedFeatures,
and use moveLayer to keep the active layer on top so stale features from
the faded-out layer don't intercept clicks.
- Skip fly-to animation on initial data load (fitBounds duration: 0)
- Replace turf.hexGrid with origin-anchored manual hex generation so
hexagons stay stable across pan/zoom instead of flickering
- Quantize zoom to integers so hex pattern only changes at discrete levels
- Scale search radius with cell size so low-zoom hexagons find their data
- Make hexagons clickable with pointer cursor; each hex shows the exact
listings it aggregated via stored search bounds
- Remove unused SEARCH_BUFFER constant
