Add MIT license (Cargo.toml + LICENSE)

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

README.md

@@ -151,10 +151,8 @@ Test fixtures live in `tests/fixtures/` (own small Rust/Python/TS repos).
 ## Licensing
 
 `rustytokens` is an independent, clean-room implementation — no code is taken
-from any AGPL-licensed project, so the project's own source is yours to license
-however you choose (MIT, proprietary, commercial, closed-source). Decide and
-set it once: add a `license` field to `Cargo.toml` and, if you ship the source,
-drop in a `LICENSE` file.
+from any AGPL-licensed project. The project's own source is licensed under the
+MIT License (see `LICENSE`); `license = "MIT"` is set in `Cargo.toml`.
 
 Dependencies are all permissive (MIT / Apache-2.0 / BSL-1.0 / Unlicense):
 `clap`, `rusqlite`, `ignore`, `rayon`, `xxhash-rust`, `serde`, `serde_json`,