YAPF v1: fast byte-aligned format, SIMD, tools and plugins

Format (version 1, replaces the earlier experimental versions):
- per-tile YCoCg-R or subtract-green colour transform, 8-bit modular
- 12 row filters per 8-row band (Left, Gradient, Up-right, Up-average,
  Up 1-8 rows), none with more than a one-add serial dependency
- residuals in groups of 8 at the group's width (w bits x 8 = w bytes),
  4-bit control codes with repeat-previous-width runs chosen by DP
- constant and stored tiles, independent 64x64 tiles, mips, GPU hints
- all sizes validated before decoding; corrupt input is rejected

Library:
- SIMD on by default: SSSE3 (runtime CPUID check; GCC, Clang, MSVC,
  MinGW) and NEON on ARM64; -DYAPF_NO_SIMD for plain C
- yapf_load_memory, yapf_load_mt, yapf_load_memory_mt
- 6-10x faster decoding than PNG (stb_image) on one core; -O2 and -O3
  builds perform the same
- fixes for macOS (sysconf) and the Windows import library exports

Tools and integrations:
- `yapf` CLI: convert PNG/JPG/TGA/BMP/PSD/GIF <-> YAPF, info, bench,
  thumbnail, mips
- JavaScript and Python bindings (byte-identical to the C encoder)
- GIMP 3 plugin: exports the flattened image, optional mipmaps
- Blender extension: import (also as plane), export, drag and drop
- VS Code preview, Figma plugin, Photoshop scripts, Linux MIME type and
  thumbnailer
- Makefile, updated build.sh / build.bat, tools/build_release.sh
- tests/test_yapf.c (784 checks) and bindings/js/test.js

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

bindings/js/README.md

@@ -0,0 +1,22 @@
+# yapf.js — YAPF in JavaScript
+
+Encoder and decoder for YAPF v1 in one dependency-free file.  Works in
+browsers, Node.js, web workers, Figma plugins and VS Code webviews, and
+produces exactly the same bytes as the C library.
+
+```js
+const YAPF = require('./yapf.js');            // or <script src="yapf.js"> → window.YAPF
+
+const img = YAPF.decode(bytes);               // Uint8Array → image
+// img = { width, height, channels, pixels, gpuFormat, flags, mipLevels, mips }
+
+const file = YAPF.encode({ width, height, channels: 4, pixels });   // → Uint8Array
+
+// draw on a canvas
+ctx.putImageData(new ImageData(YAPF.toRGBA(img), img.width, img.height), 0, 0);
+```
+
+`decode` throws an `Error` for corrupt or unsupported data.  Speed: a 4K
+image decodes in about 150 ms in Node / Chrome (the C library: 6 ms).
+
+Tests: `node test.js`.