Replace LICENSE with standard MPL-2.0 text

The previous LICENSE file contained a custom notice that automated license
detection tools could not parse. This replaces it with the standard MPL-2.0
text so that Julia General Registry and other tools can detect the license.

A note about PMPL-1.0-or-later (the author's philosophical extension of
MPL-2.0, currently in development) is appended at the end.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

Author: hyperpolymath