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/figma/README.md

@@ -0,0 +1,32 @@
+# YAPF for Figma
+
+- **Plugins → YAPF Image Format → Import YAPF image…** — choose or drop
+  `.yapf` files; each becomes a rectangle filled with the image.
+- **Plugins → YAPF Image Format → Export selection as YAPF…** — every
+  selected layer is exported at 1×, 2× or 4× and downloaded as `.yapf`.
+
+Both directions are pixel-exact: the plugin carries its own small PNG
+encoder/decoder instead of going through a canvas, which would alter
+semi-transparent pixels.
+
+## Install (development plugin)
+
+1. Use the **Figma desktop app**.
+2. **Plugins → Development → Import plugin from manifest…** and choose
+   `extensions/figma/manifest.json` (or the one inside `yapf-figma.zip`
+   from the [Releases](https://github.com/Nexoniarz/YAPF/releases)).
+3. Run it from **Plugins → Development → YAPF Image Format**.
+
+To publish it to the Figma Community, use **Publish** in the same menu;
+Figma then assigns the plugin its real `id`.
+
+## Build
+
+`ui.html` is generated: it inlines `bindings/js/yapf.js` and `src/png.js`
+into `src/ui.src.html`, because Figma loads the UI as a single file.
+
+```sh
+node build.js
+```
+
+Figma limits images to 4096 × 4096; larger `.yapf` files report an error.