Stop calling three different things "the ladder"

Oliver: "the talk about ladder and rung is extremely confusing." It was, and it
was my vocabulary, not his reading. "Ladder" had come to mean three unrelated
things in this codebase — the sequence of opponents in zombie tennis, the
sequence of WOUND STAGES on one body, and the name of a stats screen — and
"rung" meant a position in whichever of those you happened to be reading about.

One word per thing now:

  the OPPONENTS   who you play, in order, one game each (config.OPPONENTS,
                  matchFoe(n), zb.foe). Never "rungs".
  WOUND STAGES    healthy -> arm off -> headless, on one body. Unchanged, and
                  now the only thing allowed to be called a progression.
  a FAMILY        the sprite set a body wears (config.ZFAMS).

Renames: LADDER_TRAITS -> OPPONENTS, matchRung -> matchFoe, zb.rung -> zb.foe,
and the stats screen THE LADDER -> OPPONENTS FELLED, which is what it lists.

The 'L0'..'L9' record keys are deliberately NOT renamed: they are written into
saved run records, and renaming them would orphan every match anyone has
played. A comment says so where they are built.

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

src/zombies.js

@@ -491,10 +491,10 @@ function killZombie(i, quiet) {
   // down, so it earns a row. The barrel is loot and scores nothing anywhere else in the game —
   // keep that agreement here too. A chapter boss files under its DESIGN, so the screen can name
   // the one that has been killing you.
-  // A MATCH OPPONENT FILES UNDER ITS RUNG, not under the generic body it wears: the ladder screen
-  // is a list of who you have felled, and 'r' is a body, not a name. zb.rung is set by matchOpponent.
+  // A MATCH OPPONENT FILES UNDER WHO IT IS, not under the generic body it wears: the screen is a
+  // list of who you have felled, and 'r' is a body, not a name. zb.foe is set by matchOpponent.
   if (zb.variant !== 'o')
-    tally(zb.rung ? zb.rung.key
+    tally(zb.foe ? zb.foe.key
       : zb.variant === 'B' ? 'B' + Math.max(0, BOSS_ART.indexOf(zb.art))
       : zb.variant, CAUSE);
   zombies.splice(i, 1);