Make the regen pipeline check the kit, and fix the swing and toss

Every roll drifts the palette and nothing measured it: a white headband on six
frames, pale grey shorts on the toss twice, brick-red shirts and brown shoes on
the swing all sailed past --tries. check: "same"/"loose" skips colour_match, and
colour_match is a global mean/sd fit far too weak to pull brick-red back to red
— a nearest-colour palette lock is worse still, it drags the duller reds into
the racket's browns.

So _regen.py measures three numbers and a batch opts in with palette_ref:
redness (r minus mean(g,b) over saturated warm pixels — brightness alone cannot
tell brick-red from red), shorts brightness (charcoal 61 vs the drift's 83), and
the near-white fraction that is the shoes and socks (brown drops it to 0.9%,
pale shorts push it to 7.9%, correct frames sit at 2.8%). Frames known to be
right cluster tightly on all three; every drifted frame fell outside on at least
one. It rejected five bad rolls in a row, then passed a good one.

The swing also kept re-inheriting its own drift: ref_sheet is built from
[lead] + the sprites being replaced, so it was showing the generator the very
brick-red frame it was about to overwrite. Copying a canonical frame over the
targets first breaks the loop — it passed on the next roll.

Swing is now a real backswing and follow-through (silhouettes differ by 1.0,
racket low behind vs up over the shoulder), both at full standing height, and
the toss and smash wear charcoal shorts again.

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

render.js

@@ -151,7 +151,7 @@ export function proj(x, y, z) {
 
 // ---------------------------------------------------------------- sprites ----
 // assets/<name>.png; game falls back to code-drawn figures until sprites load.
-const SPRV = 76; // asset cache-buster — bump with main.js?v=N (see the img.src note below)
+const SPRV = 77; // asset cache-buster — bump with main.js?v=N (see the img.src note below)
 const SPR = {};
 for (const n of ['p_idle1','p_idle2','p_bounce','p_bounce2','p_toss','p_smash','p_run1','p_run2','p_run3','p_run4','p_swing1','p_swing2','p_die1','p_die2','p_die3','p_die4','p_die5',
                  'p_pull', // the serve wind-up: the racket dropping behind him while the pull is drawn