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/vscode/media/preview.css

@@ -0,0 +1,26 @@
+html, body { height: 100%; margin: 0; }
+body {
+  display: flex; flex-direction: column;
+  background: var(--vscode-editor-background, #1e1e1e);
+  color: var(--vscode-foreground, #ccc);
+  font: 12px var(--vscode-font-family, system-ui, sans-serif);
+}
+#bar {
+  display: flex; justify-content: space-between; align-items: center; gap: 12px;
+  padding: 6px 12px; border-bottom: 1px solid var(--vscode-panel-border, #333);
+}
+#bar select {
+  background: var(--vscode-dropdown-background, #3c3c3c);
+  color: var(--vscode-dropdown-foreground, #ccc);
+  border: 1px solid var(--vscode-dropdown-border, #555);
+}
+#stage { flex: 1; overflow: auto; display: grid; place-items: center; padding: 16px; cursor: zoom-in; }
+body:not(.fit) #stage { cursor: zoom-out; }
+canvas {
+  background-color: #fff;
+  background-image: conic-gradient(#ccc 25%, #fff 0 50%, #ccc 0 75%, #fff 0);
+  background-size: 16px 16px;
+  box-shadow: 0 0 0 1px var(--vscode-panel-border, #333);
+}
+canvas.pixelated { image-rendering: pixelated; }
+#error { padding: 16px; color: var(--vscode-errorForeground, #f48771); }