GetOrbitPosition's step-time fill and RailAt each decided the rail chain (root at
FixedPosition, child at parent plus offset). The fill is now RailAt(id, _time).
DrawnPoseTests builds the sun on an off-centre FixedPosition (the ZoneGenerator
cluster-root shape) and adds a root test at step and drawn time, and an unset-orbit
OrbitalEntity fact for the DrawAhead guard.
All commits build, unverified until the job in the report.
Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>