physical lighting, volumetric clouds, terrain shadows, pixel-art render scale

- atmosphere: physical terrain lighting (air mass, Rayleigh beam colour,
  skylight, moon, starlight floor), aerial perspective for terrain and
  cloud deck, configurable haze/albedo/ambient gains
- clouds: march the deck in height instead of ray distance, IGN dither
  (no per-frame flicker), per-step height jitter, 4-octave fbm renormalised,
  softer density threshold, distance softening as a procedural mip,
  grazing path clamp, cloud shadows on the ground (cloudShadowDensity/
  Floor/Ambient) and cloud haze factor
- terrain: self-shadows from the elevation field (penumbra + shadow floor),
  soft mosaic rim (edgeFadeTiles), east/west axis corrected (+X = west)
- lights: per-object twilight switching for cars, city dots and ground blocks
- flights: contrail width 620 m, fade to zero by contrailFadeKm, aircraft
  size decoupled from trail width, count halved
- render: CONFIG.renderScale with integer upscale + image-rendering: pixelated
- data: nginx overpass proxy + cache, per-mirror cooldown ladder, ring-based
  cell ordering (disc fills evenly), settlements fetched before roads,
  interim chain persistence, two worker lanes (car/city) with progress logs
- removed: NASA VIIRS night-lights layer (fetch, canvas, texture, uniforms)

overpass-cache.conf

@@ -0,0 +1 @@
+proxy_cache_path /var/cache/nginx/overpass levels=1:2 keys_zone=overpass:20m max_size=2g inactive=30d use_temp_path=off;