Byte-accurate entries for the three water sections (transitional
per-body level rule, provisional salinity, WSRF sentinel/quantization),
updated size math (~576 MiB at 8K with water), the on-the-record
rationale for NOT serializing basins, and README updates for the new
pipeline stage, the 0_water snapshot, and the SkipRoads toggle.
Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>