pathways: chevrons only for free directions, fade while previewing, re-render nav on placement

- chevron is only drawn when the direction is not already occupied, so it
  never overlaps a neighboring photo
- hovering a free direction adds a .preview class to the zone so the chevron
  fades out while the ghost preview shows underneath it
- pointermove on an occupied direction early-returns (no ghost, no fade)
- refreshAllNav re-renders every tile's nav after a placement so stale chevrons
  disappear as soon as a direction becomes occupied

0 files changed, 0 insertions, 0 deletions