fairy-stockfish browser opponent

Pinned upstream source: https://github.com/fairy-stockfish/fairy-stockfish.wasm/tree/4d4b39395955df4695f28887800f0836f9c4d37d
Modified corresponding source: source.zip (served alongside this notice).
Build instructions and changes: BUILD.txt; upstream-changes.patch.
Browser worker adapter: worker.js.

Emscripten 3.1.51, C++17, classical evaluation (no NNUE network).
Unzip source.zip, activate Emscripten, then:
make -C fairy/src -j4 build ARCH=wasm embedded_nnue=no minify_js=no largeboards=yes OS=Linux KERNEL=Linux assertion=yes
Changes: synchronous single-thread search in thread.cpp/thread.h, ordinary stdin UCI loop,
4 MiB stack, explicit incoming JS API; no pthread/proxy/async JS loop, removed obsolete compiler flag.
The original build Makefile still links libpthread stubs; no WebAssembly shared memory is used.
variants.ini in this distribution defines the standard seven-column, six-row Four in a Row game.

SHA-256 inventory:
BUILD.txt: baef9e2aae1e7106f538290494309d320f55b988e4b182fccd2473f3a0910a16
Copying.txt: 0b383d5a63da644f628d99c33976ea6487ed89aaa59f0b3257992deac1171e6b
source.zip: ac9f1cf88175edbc6bb7d15acac54eba55b88fb6d4a01005cd639dfdb499ef95
stockfish.js: d88261087a828fe932f3fcbaa7aec05a96301b1e0337ebd9b387efe26e20d276
stockfish.wasm: d725d56d85ec9e8092b1728204813f6ad8564ac2355dcf7ece2a950e3be0c622
upstream-changes.patch: 1d28da60de087e4d3013358f93f1027ffcfe5cfb356a39dcc2d660ca4f68052e
variants.ini: 50e0d470c824dc928f67f2f6c376f21e32baba204c313a793e77274a5a9d4380
worker.js: b6b94e83268a029537279f29f82138c4f488ca97890959afaa452c23b9117fa6