- LazyMount: mount a grid card only when it scrolls within 600px (skeleton-space
placeholder otherwise), so a long feed no longer mounts every card + its
hooks/DOM up front. Falls back to immediate render without IntersectionObserver.
- GearSwapItemCard: clicking the card now opens /listing/:pubkey/:identifier
(was opening a DM). 'Contact Seller' still opens the DM. Card set to h-full so
the lazy wrapper keeps the equal-height grid.
Gate: 101 tests, 0 errors/warnings, boot smoke green.
