Art: SVG -> 48x48 portrait converter, and it works

Magnific's SVG export is flat-shaded vector (~550 solid-fill paths, 6
gradients), which converts to pixel art cleanly. tools/svg2portrait.py
rasterises at 16x the target via qlmanage, then takes the most common
colour per 16x16 block — a true pixelate with no blending — and maps to
the 11-colour portrait palette.

Measured on Aki: 19 colours after pixelate, 10 after palette, visually
near-identical. So the portrait palette is sufficient for this art.

Contrast with the bitmap route this replaces: a 48x48 PNG resized in
Photoshop had 1330 unique colours in 2304 pixels, because bicubic
resampling turns flat regions into gradients. Quantising that speckled
badly across the blazer and background.

Also adds tools/pixtool.py — dependency-free PNG decode/encode (no Pillow
on this machine) plus the palette table shared with kissaten.c.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

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