Splatter: clear the wave by hand, tougher 2-hit shamblers, set cards, free depth

Feedback batch from a phone playtest:

- Winning a game no longer auto-sweeps the court. The survivors stay and must
  be killed by hand (no new spawns, no scoring during the mop-up); only once the
  court is clear does play advance to the changeover / next game / set. Replaces
  sweepCourt() with a G.clearing gate + proceedAfterClear(). "CLEAR THE COURT".
- Classic shamblers (a/b) now soak one splat-quality wound before they drop
  (shamblerHp=2) — swapping to new z_aw/z_bw wound skins that bleed the thin
  dynamic trickle plus a small impact pop. Only the runner stays one-shot glass;
  brute/boss unchanged. Ball, pellets and triple side-balls all respect hp.
- Winning a SET shows a centered milestone card (a real pause) before the horde;
  one reusable drawCard() now backs both it and the reworded sudden-death card.
- Player is no longer pinned to the baseline: free to advance up-court on
  keyboard (bounded at the net); touch keeps the baseline (drag is the serve-aim)
  and the horde/GUN burst re-brace there.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

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