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/gimp/README.md

@@ -0,0 +1,48 @@
+# YAPF for GIMP
+
+Open and export `.yapf` images in **GIMP 3.0 or later**.
+
+- **File → Open** reads `.yapf` (Gray, Gray + Alpha, RGB, RGBA).
+- **File → Export As… → `name.yapf`** writes the visible image (layers are
+  flattened into a copy; your document is untouched), with an optional
+  **Store mipmaps** checkbox for game engines.
+
+## Install
+
+You need GIMP 3 with its development files (`gimptool`).
+
+| System          | Development files                                   |
+| :-------------- | :-------------------------------------------------- |
+| Arch / Manjaro  | `sudo pacman -S gimp` (includes them)               |
+| Debian / Ubuntu | `sudo apt install libgimp-3.0-dev` (GIMP 3 packages) |
+| Fedora          | `sudo dnf install gimp-devel`                       |
+| Windows         | MSYS2: `pacman -S mingw-w64-ucrt-x86_64-gimp`        |
+| macOS           | build GIMP 3 from source or use MacPorts/Homebrew   |
+
+Then, from this folder:
+
+```sh
+gimptool --install yapf-gimp.c
+```
+
+That compiles the plugin (it pulls in `../../yapf.c` itself) and installs it
+into your personal GIMP plug-ins folder.  Restart GIMP.
+
+### Manual build
+
+```sh
+gcc -O2 $(pkg-config --cflags gimpui-3.0) yapf-gimp.c $(pkg-config --libs gimpui-3.0) -o yapf-gimp
+```
+
+Copy `yapf-gimp` to `<GIMP config>/plug-ins/yapf-gimp/yapf-gimp`, where the
+GIMP config folder is `~/.config/GIMP/3.0` on Linux,
+`%APPDATA%\GIMP\3.0` on Windows and
+`~/Library/Application Support/GIMP/3.0` on macOS.
+
+## Notes
+
+- Pixels are saved with the sRGB flag, because GIMP's 8-bit buffers are
+  gamma encoded.  Files marked linear load as linear.
+- When a file has mipmaps, GIMP opens the full-size image.
+- Tested with GIMP 3.0.8 on Linux: opening matches the reference decoder
+  pixel for pixel, and export equals GIMP's own flattened PNG of the image.