fix(licence): set top-level LICENSE to MPL-2.0 (owner-directed) (#354)

## What

Sets **standards'** top-level `LICENSE` to **MPL-2.0** (owner-directed
2026-06-02). The file previously declared `AGPL-3.0-or-later` with a
body that didn't match any licence template.

## Scope — LICENSE file only (no SPDX sweep)

`standards` is a **deliberately multi-licensed** repo —
`PMPL-1.0-or-later` dominates its spec/template content (3644 files),
alongside MPL-2.0, MIT, AGPL, Palimpsest-0.4, and CC-BY-SA. This PR
changes **only the top-level `LICENSE` file**; **per-file
`SPDX-License-Identifier` headers are intentionally left untouched** (no
bulk SPDX sweep, per the estate no-sweep mandate). The repo's mixed
per-file licensing is preserved exactly as-is.

Verified locally: `check-licence-consistency.sh` → **`[OK] Licence
consistency check passed`** (standards has no root build manifest, so
the gate validates the `LICENSE` SPDX + body alone; both now resolve to
MPL-2.0).

---
_Generated by [Claude
Code](https://claude.ai/code/session_01GsJX13UjwiBk9hkddqvYMh)_

Co-authored-by: Claude <noreply@anthropic.com>

Author: hyperpolymath