feat(accent): pick the colour that stands out, not the average

colorz returned cluster means, which averaged a small vivid element into
its surroundings, so a violet motif on a frame of pale skin came out as a
muddy red. signature_color() now reads the pixels of a 256px thumbnail
itself and scores each by chroma times its distance from the image's mean
colour. The top 2% vote by hue, neighbouring bands summed, and the most
vivid pixel near the peak is snapped. A pick under chroma 25 is a tint and
takes the fallback.

Dropping colorz also fixes two bugs. Its k-means seeds are random, so one
wallpaper could snap differently between runs. And it calls sys.exit() on
some images, which `except Exception` in main() does not catch, so
udt-accent died without writing and the previous accent stayed.

Over 314 wallpapers: no errors (colorz failed on 18), 25 fall back,
about 0.06s each. The selftest gains a small-vivid-patch case and a
grey-image case.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

1 files changed, 11 insertions, 2 deletions

diff --git a/AGENTS.md b/AGENTS.md
index 55bdf2d..afb685a 100644
--- a/AGENTS.md
+++ b/AGENTS.md
@@ -239,8 +239,17 @@ which would move every cache on the system, so `udt-accent` writes the real
 file to `~/.cache/udt/` and `install.sh` symlinks the old path at it. That
 directory now holds the link and nothing else.
 
-**Extraction is deliberately isolated from pywal's cache.** It calls
-`pywal.backends.colorz.get()` directly, which returns a list and writes nothing.
+**The accent is what stands out, not what dominates.** `signature_color()`
+reads the pixels itself (PIL, on a 256px thumbnail) and scores each by chroma
+times its distance from the image's mean colour; the top 2% vote by hue. It
+replaced pywal's colorz backend, whose cluster means averaged a small vivid
+element into its surroundings, whose random seeds made one wallpaper snap
+differently between runs, and which `sys.exit()`s on some images, which
+`except Exception` did not catch, so the old accent stayed. A pick below
+chroma 25 is a tint, and takes the fallback.
+
+**Extraction is deliberately isolated from pywal's cache.** It reads pixels
+and writes nothing.
 Running `wal -i` instead would rewrite all of `~/.cache/wal`, including the
 terminal's ANSI colours, and that is the exact failure this design exists to
 avoid. If you change `signature_color()`, verify it still writes nothing.