feat(simulation): region climate tier — baseline + district modulation + edge fuzz (T-1078)

Introduces the region (~205 km) climate tier per D-243 §3/§4, above the
DistrictProfile carrier. New region_profile.rs: RegionProfile/RegionClock,
derive_region_baseline_c (latitude lerp + greenhouse, D-240 class-envelope,
no orbit/star inputs), and region_baseline_at_district — the D-243 §4
edge-fuzz warp-perturbed bilinear blend of surrounding region baselines so
the ~205 km grid is invisible in the output.

Splits district temperature (D-243 §3): derive_district_temperature_c now
modulates the region baseline with elevation lapse only, replacing the
from-scratch per-district derivation. build_district_profile takes an
Option<f32> region baseline; None preserves the legacy single-phase path
(existing call sites unchanged). derive_cover (voxel.rs) consumes the
post-refactor value with no signature change.

Region clock (season/weather) scaffolded; transient tick callbacks deferred
to Q-105 per the two-phase convention. 14 region_profile + 5 district
modulation tests added.

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

server/src/atlas/mod.rs

@@ -21,6 +21,7 @@ pub mod heightmap;
 pub mod layer1;
 pub mod layer_proxy;
 pub mod plugin;
+pub mod region_profile;
 pub mod road_graph;
 pub mod scale;
 pub mod skeleton_gen;