Toolweb AVIF image conversion

The AVIF encoder is @jsquash/avif version 2.1.1, released under Apache-2.0.
Package: https://www.npmjs.com/package/@jsquash/avif/v/2.1.1
Upstream: https://github.com/jamsinclair/jSquash/tree/main/packages/avif
The package's encoder and supporting code are derived from Google's Squoosh project.
Original supporting code: Copyright 2020 Google Inc.; modifications by Jamie Sinclair.
The complete package license is supplied at /vendor/AVIF-LICENSE.txt.

The codec documentation identifies libavif v1.0.1:
https://github.com/AOMediaCodec/libavif/tree/v1.0.1
Its license is supplied at /vendor/LIBAVIF-LICENSE.txt.
The libavif license includes its related third-party codec notices. The upstream
libaom license and patent notice are also supplied at /vendor/LIBAOM-LICENSE.txt
and /vendor/LIBAOM-PATENTS.txt.

Toolweb's wrapper uses the unmodified, single-thread encoder module and its
self-hosted WASM binary. Toolweb does not claim authorship of those components.
No photo or file contents are sent to the upstream maintainers or any codec CDN.

Encoding is initiated explicitly in a dedicated worker, within local pixel and
time limits. The wrapper and its bounds are application code, not an upstream
guarantee of compression ratio, processing duration or decoder compatibility.