Stabilize sapling-wasm with authoritative vectors and warning gates

[jevonearth]

Summary

• add MIT licensing and a security policy, and document provenance and the AirGap fork lineage
• tighten repo verification scripts and package metadata for the published npm workspace
• add authoritative Zcash and Octez vector coverage plus Node-side characterization tests
• gate the Rust crate on warnings and trim noisy re-exports so the checks stay meaningful

Verification

• npm run build
• npm test
• npm run test:repo
• cargo test --manifest-path packages/sapling/Cargo.toml octez
• cargo fmt --manifest-path packages/sapling/Cargo.toml