test(simulation): believability + budget verification harness (T-1031)

D-239 §1/§8/§9/§10 verification harness (server/tests/derivation_harness.rs):
golden-seed determinism regression, §8 binding-law sweeps (drainage monotonicity,
lithology->landform, glaciation->form no-glacial-U-at-grade-0, climate->vegetation
no-skip + riparian), per-family <5ms/chunk budget assertion, and validation-case
bodies (Kallast=alluvial pass; Velen/Gruenfeld skipped-not-in-wiki). Exposes
derive_morphology_zone as pub for the integration test.

NOTE: golden file not yet generated + fixtures predate the T-1033 BodyParams strip;
fixed in follow-up commits after merging main.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

server/src/atlas/region_profile.rs

@@ -497,7 +497,7 @@ pub fn derive_river_threshold(tectonic: TectonicClass, precip: PrecipitationClas
 ///   - BraidedPlain (§6) is NOT emitted at region scale — distinguishing it from Delta needs a lithology signal (§8 Gravel→braided) RegionProfile lacks; deferred to ChunkContext (see the D-239 §6 implementation note).
 ///
 /// D-010: all gates are integer comparisons. No float arithmetic in this function.
-fn derive_morphology_zone(
+pub fn derive_morphology_zone(
     tectonic: TectonicClass,
     glaciation: GlaciationGrade,
     slope_q: i32,