Relicense from PolyForm Noncommercial to MIT OR Apache-2.0 (#158)

Relicenses Wickra from PolyForm Noncommercial 1.0.0 to the dual, OSI-approved **MIT OR Apache-2.0** (the de-facto Rust convention). Wickra becomes permissive, commercial-use-permitted open source; users may choose either license.

## Changes
- Replace `LICENSE` (PolyForm) with `LICENSE-MIT` + `LICENSE-APACHE` (full texts).
- Cargo: workspace `license = "MIT OR Apache-2.0"` (SPDX) + all 7 sub-crates switched from `license-file.workspace` to `license.workspace`.
- `deny.toml`: drop PolyForm from the allowlist.
- Python: `pyproject.toml` PEP 639 SPDX expression; remove the non-commercial classifier (verified: sdist metadata emits `License-Expression: MIT OR Apache-2.0`).
- Node: `package.json`, the 6 platform manifests and both lockfiles.
- README + Python/Node/WASM binding READMEs, CONTRIBUTING, CITATION.cff, PR template, and the WASM `pkg.license` step in `release.yml`.
- SECURITY.md: refresh supported versions 0.1.x -> 0.4.x.
- CHANGELOG: note the relicense under [Unreleased].

## Notes
- No code changes; metadata/text only. `cargo build` and `cargo deny check licenses` pass locally.
- GitHub will auto-detect "MIT, Apache-2.0" once this lands (currently NOASSERTION).
- Matching downstream changes (org `.github` profile, webpage, docs) are in separate PRs; merge those together with the relicense release so the live sites and org profile do not claim MIT before the packages do.

CONTRIBUTING.md

@@ -5,11 +5,11 @@ build the project, the standards a change must meet, and how to get it merged.
 
 ## License of contributions
 
-Wickra is licensed under the **PolyForm Noncommercial License 1.0.0** (see
-[`LICENSE`](LICENSE)). By submitting a contribution you agree that it is
-licensed to the project under those same terms. The Noncommercial license
-permits use for any purpose **other than** a commercial one; keep that in mind
-when proposing features or depending on Wickra elsewhere.
+Wickra is dual-licensed under the [MIT](LICENSE-MIT) and
+[Apache-2.0](LICENSE-APACHE) licenses; users may choose either. Unless you
+explicitly state otherwise, any contribution you intentionally submit for
+inclusion in the work, as defined in the Apache-2.0 license, shall be dual
+licensed as above, without any additional terms or conditions.
 
 ## Project layout