refactor: rebuild natal query API around domain models

[lzm0x219]

Summary

• Move natal creation and read-only query behavior into the owning domain model modules.
• Replace the standalone query/ziwei implementation with Natal, ReframeScope, ScopedPalace, ScopedStar, and DecadeScope APIs.
• Add public black-box and integration coverage for scoped queries, decade navigation, palace relations, stars, and transformations.
• Align testing guidance and changelog with the new API boundaries.

Validation

• mise run check
• zig fmt --check build.zig build.zig.zon src tests benchmarks
• zig build
• zig build test
• zig build benchmark-docs-check

Commits

• refactor(domain): move query API into domain models
• test(integration): cover scoped natal queries
• docs: document natal query API refactor