Palette-quantize generated brand PNGs (#25)

* docs: design brand PNG optimization

Palette-quantize generated PNGs (Pillow FASTOCTREE) in raster.py — ~70-80%
smaller, visually lossless for flat art, alpha preserved on transparent marks.
SVGs and external optimizers out of scope.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

* docs: implementation plan for brand PNG optimization

Two tasks: add Pillow + the FASTOCTREE quantize step in raster.py (with tests and
regenerated PNGs), then docs/finalize.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

* feat(brand): palette-quantize generated PNGs (Pillow FASTOCTREE)

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

* test: convert to RGBA to avoid PIL tRNS warning

* docs(brand): document PNG quantization

* docs: correct uv.lock note in png-optimization spec (repo tracks it)

* docs: scope the PNG shrink claim to large assets

* build: sync optimized social card into docs/assets (served og:image)

---------

Co-authored-by: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

Author: lesnik512

architecture/brand-marks.md

@@ -2,6 +2,21 @@
 import subprocess
 from pathlib import Path
 
+_PNG_COLORS = 32  # palette size; flat art needs few (8 already looked clean; 32 = headroom)
+
+
+def _quantize_png(path: Path, colors: int = _PNG_COLORS) -> None:
+    """Re-save a PNG as an indexed-palette image — visually lossless for flat
+    art. FASTOCTREE preserves alpha, so it is correct for both the opaque
+    social cards and the transparent marks. No-op if Pillow is unavailable."""
+    try:
+        from PIL import Image
+    except ModuleNotFoundError:
+        return
+    im = Image.open(path).convert("RGBA")
+    q = im.quantize(colors=colors, method=Image.Quantize.FASTOCTREE)
+    q.save(path, format="PNG", optimize=True)
+
 
 def export_png(
     svg_path: Path,
@@ -20,4 +35,5 @@ def export_png(
         args += ["-h", str(height)]
     args += [str(svg_path), "-o", str(png_path)]
     subprocess.run(args, check=True)
+    _quantize_png(png_path)
     return True