Relicense to Apache-2.0 #75

The maintainer's decision (2026-10-03, every thisisthepy project): Apache-2.0 replaces MIT. Done when LICENSE holds the Apache License 2.0 text, pyproject's SPDX license is Apache-2.0, the README badges and license lines (EN/KO) and the guide footers say so, and the wheel still builds. The published 0.1.0a1 stays MIT; the change applies from the next version.