Implement Slice 4 transformation selection

[sidmohan0]

Summary

• canonize and implement the Slice 4 transformation configuration envelope
• add entity selection, per-entity overrides, exact and full-match regex allowlists, validation limits, and structured errors
• expose the same contract through Rust, Python, Node, and WASM, including scan locale plumbing
• update public types, examples, and installed-package contract tests

Verification

• cargo test --workspace (47 tests passed)
• cargo clippy --workspace --all-targets -- -D warnings
• npm run test:package --prefix bindings/node
• npm run test:package --prefix bindings/wasm
• built and installed the Python abi3 wheel, then ran bindings/python/tests/test_installed.py
• git diff --check