chore(license): migrate to MPL-2.0 (#38)

## Summary
Migrates this repo's license declaration from `PMPL-1.0-or-later` to
`MPL-2.0`.

**Rationale:** solo.

## Changes
- LICENSE file replaced with canonical `MPL-2.0` text (including SPDX
header).
- Package metadata updated where present (Cargo.toml, package.json,
deno.json, mix.exs, pyproject.toml).

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

Author: hyperpolymath

Cargo.toml

@@ -15,7 +15,7 @@ resolver = "2"
 version = "0.1.0"
 edition = "2021"
 authors = ["Jonathan D.A. Jewell <j.d.a.jewell@open.ac.uk>"]
-license = "PMPL-1.0"
+license = "MPL-2.0"
 repository = "https://gitlab.com/hyperpolymath/wharf"
 description = "The Sovereign Web Hypervisor - Immutable CMS Infrastructure"