Seam badge, and a pasteable cosmetics.json entry - #9

The preview now says whether a pattern shows a seam once the game tiles it:
Seamless, Slight seam, or Visible seam.

The metric is subtler than it looks, which is why this is a port rather than a
re-derivation. A correctly-tiling periodic pattern legitimately has a hard
transition at the wrap — period-8 stripes on a 32-wide canvas put a stripe
boundary exactly there. What makes a seam visible is the wrap being an OUTLIER,
so it is ranked against the 90th percentile of the pattern's own interior
transitions rather than their mean; the mean is dragged down by the many
identical column pairs inside a periodic pattern, which is what made an earlier
version flag 17 of 28 correctly-tiling patterns.

It also carries the rhythm check, which local adjacency cannot do: period-7
stripes on a 32-wide canvas make a perfectly ordinary-looking edge while the
cadence breaks on tiling. Driven in the app, that case reports Visible seam and
a checkerboard reports Seamless.

Scoring walks the bitmap several times looking for its intrinsic period, so it
settles 250ms after a stroke rather than running on every pointermove.

The DSL fixture now carries both scores and the label for all 62 programs, and
the suite compares them to 1e-9 — pinning the numbers rather than just the
verdict, so a port that lands on the right label by luck still fails. All three
verdicts appear in the corpus.

Export gains the cosmetics.json entry: the file keys patterns by their encoded
data, so the entry is that key and a name, slugified. role_group is entitlement
metadata the game assigns and a new pattern does not claim it.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01UCrKKTD2mwHx8Fm1EnJiQ3