chore(license): migrate proprietary → LicenseRef-Proprietary-AllRightsReserved (covert IP) (#23)

Replace LICENSE file with canonical LicenseRef-Proprietary-AllRightsReserved text and update package
metadata (Cargo.toml/package.json/deno.json/mix.exs/pyproject.toml where
present) to declare the new SPDX identifier.

Rationale: covert IP.

Part of estate-wide metadata cleanup 2026-05-26.

Author: hyperpolymath