Address the doc/test-correctness items from PR #149 review:
- cascade.rs: Layer 3 is RNG-free (pure fn of attractors+cities); it does
not consume the carried SeedChain. Corrected the "first RNG-using layer"
claims on the module doc and the Settlement variant (Hoshe H3).
- cascade.rs: layers_are_ordered now also asserts Topography < Settlement,
pinning the invariant the up_to >= Settlement guards rely on (Tyre T2).
- features.rs: strength is an integer 0-100 (quantized at extraction), not
f32, and consumers that rank by it use the integer value (Hoshe H2).
- layer_proxy.rs: AtlasLayerRequest.up_to is not yet honored — run_work_item
runs through Settlement unconditionally; per-request depth deferred to
#1021 (Tyre T1).
Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>