v3.1.0

Ports what matters from upstream Arnis 3.1.0 (90 commits, 17 pull requests),
and fixes several things that were quietly broken.

Fixed

• Overture buildings were never placed. Release discovery had rotted and the
  fallback release was retired, so every request 404'd. Rural areas lost every
  building OSM does not map. Releases are now found from the bucket listing.
• Cut-off OpenStreetMap responses were treated as complete. A query that runs
  out of time still returns valid JSON, just missing most of the area. Those
  responses now fail over to the next server instead of building a half-empty world.
• Extended-height worlds froze the day and night cycle on 1.21.9 and newer.
  /time set did nothing. The datapack no longer ships the deprecated key that
  caused it.
• Terrain smoothing was off centre by half a cell on both axes, in every
  terrain render.
• Dams, weirs and culverts were drawn as open water, so a barrage got a river
  running across the top of it and a culvert cut a channel through its own bank.
• A bad --bbox crashed instead of explaining itself.
• Barriers tagged material=wood now render as oak fence.
• The update check pointed at upstream, so the fork kept offering you a version
  with none of its own features.
• Software rendering is no longer forced on Linux, which fixes EGL_BAD_PARAMETER
  on some Wayland and AMD setups.

Added

• --scale is validated. Values outside 0.01 to 4.0, plus NaN and infinity, are
  rejected up front instead of producing an empty or hung run.
• A golden world hash test harness with five committed OpenStreetMap fixtures,
  covering a European old town, a US suburb, Manhattan, a medina and subarctic
  Finland. Generation changes are now measurable rather than eyeballed.

Not taken

Upstream 3.1.0 skips every building, road and rail below scale 0.3. That would
empty every render at 1:10, so it is deliberately not ported. A test guards it.

Image signage is also held back: it writes map data per cell, which does not
survive a multi cell merge.