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>

extensions/linux/install.sh

@@ -0,0 +1,18 @@
+#!/bin/sh
+# Registers the YAPF MIME type and thumbnailer for the current user, so file
+# managers that use freedesktop thumbnailers (GNOME Files, Nemo, Caja,
+# Thunar with tumbler) show .yapf previews.  Needs `yapf` on your PATH.
+#   sh extensions/linux/install.sh            (current user)
+#   sudo sh extensions/linux/install.sh --system
+set -e
+here=$(cd "$(dirname "$0")" && pwd)
+if [ "$1" = "--system" ]; then data=/usr/share; else data=${XDG_DATA_HOME:-$HOME/.local/share}; fi
+
+command -v yapf >/dev/null 2>&1 || echo "warning: 'yapf' is not on your PATH; thumbnails need it" >&2
+
+mkdir -p "$data/mime/packages" "$data/thumbnailers"
+cp "$here/yapf-mime.xml" "$data/mime/packages/yapf.xml"
+cp "$here/yapf.thumbnailer" "$data/thumbnailers/yapf.thumbnailer"
+update-mime-database "$data/mime" >/dev/null 2>&1 || true
+echo "Installed the image/x-yapf MIME type and thumbnailer into $data"
+echo "Restart your file manager (e.g. 'nautilus -q') and clear ~/.cache/thumbnails/fail if needed."