feat(pocket3d-world): add world law runtime - #310

Summary

• add deterministic hidden state, weighted relations, spatial fields, deferred law transactions, snapshots, and hashes
• add local opposing-field interference and a finite spherical barrier projection into ordinary physical impulses
• preserve a shared energy invariant without entity, tag, recipe, character, or scenario branches

Validation

• cargo fmt --manifest-path engine/Cargo.toml --package pocket3d-world -- --check
• cargo test --locked --manifest-path engine/Cargo.toml --package pocket3d-world -- --test-threads=1 (30 passed)
• cargo clippy --locked --manifest-path engine/Cargo.toml --package pocket3d-world --all-targets -- -D warnings
• barrier invariant covered across two mass, speed, and collider-extent configurations