Camera speed was 0.45 units/sec which on 13km/tile tiles = ~5850
km/h = supersonic. User reported flying through tiles too fast.
- drift speed 0.45 -> 0.12 units/sec (~1500 km/h, fast plane)
- corridor 15 -> 25 tiles along travel (~3.5 min between refetches
at uSpeed=1, instead of ~12 sec)
- buffer 2 -> 3 tiles (refetch starts earlier so we always have
tiles loaded before the camera reaches the edge)
- Updated JS-side drift calculation to match the new shader speed
Camera now leisurely follows the corridor; refetch only once every
couple of minutes.