feat(atlas): add one canonical Greater Realm continent pipeline

[ael-dev3]

Summary

Builds the private, deterministic generation and review pipeline for one canonical Greater Realm world.

• creates one organic continent candidate rather than multiple parallel worlds
• adds hierarchical terrain shaping with broad low-frequency terraces, short traversable ramps, and bounded weathered fBM-style detail
• preserves coastline sign, Lowlands reserve constraints, hydrology, political regions, mountain gates, and Tier-II connectivity
• adds analytical height atmosphere for private hillshade review, with independent extinction and in-scattering so valleys hold denser haze while peaks remain readable
• keeps all seeds, coordinates, atlas payloads, and review images inside the owner-private workspace
• strengthens fail-closed validation, scratch-buffer zeroization, toolchain attestation, deterministic packaging, and public-boundary enforcement

The terrain/atmosphere approach is informed by the SimonDev Customizing Materials demo and the analytical height-fog model documented in the SIGGRAPH 2006 course notes. No third-party source code was copied.

Scope guard

This PR does not activate the Greater Realm in the live client, publish a SpacetimeDB world revision, change production schemas, deploy Pages, or expose private generation artifacts. Selection and production activation remain separate owner-controlled steps.

Validation

• Greater Realm suite: 18 files / 225 tests passed
• focused terrain, authority, and zeroization regression: 19 tests passed
• TypeScript project build passed
• private candidate package generated and independently verified
• private visual review found no blocking silhouette, topography, hydrology, or region defect
• atlas public-boundary check passed
• file-size and license policy checks passed
• pinned toolchain preflight passed
• dependency install reported 0 vulnerabilities