feat(battlenode): mulligan+turn ops track on engine state (M-HC-1)

Task 2's WireMulliganPhase already installed the full mulligan delegate
set (Swap/Ready, not just Deal) via MulliganEventSetting, and the
mulligan + turn-draw mutations flow through VfxMgr.RegisterSequentialVfx
— which HeadlessConductorVfxMgr runs for InstantVfx. So Swap/Ready/
TurnStart/TurnEnd resolve headless with ZERO new shim/seed/view fills.

Adds the M-HC-1 milestone assertions: a mulligan-swap test (post-swap
hand holds deck idx 1,2,4 — idx-3 swapped for the next unused idx) and a
two-turn test (Deal->Swap->Ready->TurnStart/TurnEnd x2) asserting the
engine's deterministic node-native progression on both seats
(hand/deck/PP/turn/leader-life) at each boundary. Frame shapes mirror the
captured battle_test_cl1 receive stream (self/oppo pos-idx lists, spin).

Harness/node: +DeckCount/Turn board-state pass-throughs (test reads).

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

SVSim.BattleNode/Sessions/Engine/SessionBattleEngine.cs

@@ -149,6 +149,8 @@ internal sealed class SessionBattleEngine
     public int LeaderLife(bool playerSeat) => Seat(playerSeat).Class.Life;
     public int Pp(bool playerSeat) => Seat(playerSeat).Pp;
     public int HandCount(bool playerSeat) => Seat(playerSeat).HandCardList.Count;
+    public int DeckCount(bool playerSeat) => Seat(playerSeat).DeckCardList.Count;
+    public int Turn(bool playerSeat) => Seat(playerSeat).Turn;
 
     /// <summary>Followers in play, excluding the leader (the Class card occupies one slot of
     /// ClassAndInPlayCardList).</summary>